Tension. That's the word that sums up my childhood. In many ways I was happy, but the home I shared with my close-knit family - Mama, Dada and my brother, Roger - was a place of tension, and sometimes terror.

My mother ran a small sweet shop in Maidstone in Kent, and Dada, an ex-regular army sergeant, had a milk round to bring in extra money.

Part of the problem was that our house was tiny: at the back of the shop a small downstairs kitchen; narrow, dark stairs up to a small front room; and just two bedrooms. The walls were thin, and there was seldom a lock on the lavatory/bathroom door because it was always being broken - by Roger, who could burst in on you at any moment.

Roger and I had to share a bedroom with just a curtain separating our single beds. Some nights I would be woken by heavy breathing to find the curtain pulled back and Roger sitting on the edge of his bed smoking a cigarette and staring at me. Nothing worse ever happened, but it was eerie, unsettling. I would often go to bed fully dressed.

Roger, born in 1939, two-and-a-half years before me, was always a difficult child. At school he was excessively shy: he spoke to no one and spent miserable, tortured playtimes hiding in corridors or lavatories for fear of being spoken to. At home he was disobedient, noisy and quarrelsome - he lived his life through just the four of us.

We didn't know then what was wrong with him; nobody did, not even the doctors. You couldn't quite put your finger on it, but you knew Roger was disturbed, tormented and unhappy. I suppose other people described him as "odd", but if they did they never told me, they just stayed clear of us.

When I was 17 we moved to Southampton, where my parents took over a newsagent's on a council estate and we all lived in the small flat above. Everything continued to revolve around Roger and his moods. When he came down into the shop looking fierce and dishevelled, we worried he'd be rude to customers or shout at the children. Upstairs, if he was asleep, we would tiptoe around him, petrified that if he woke up he would be trouble. Once awake, Roger would sit drinking endless cups of tea, playing his records louder and louder - Elvis was his favourite - convinced he could hear his name in the lyrics. He was so unutterably lonely.

Roger was 23 when he was finally diagnosed as suffering from paranoid schizophrenia - "a typical case", the psychiatrist said.

I remember it all very vividly. We were in the kitchen; there was the gentle, comforting sound of crockery being laid on the table and the kettle singing; Roger was upstairs in his bedroom; we were having a peaceful interlude. Suddenly the air was rent with the violent noise of screaming and horrific retching from above. We could hear Roger racing up and down his room. Mama rushed up calling his name, but his door was locked. "Leave me alone, leave me alone," he shouted. Then the door was suddenly flung open. His eyes blazing in his white face, Roger held up his fist and shouted: "I'll get you, I'll win; you know who I am don't you?"

Roger saw various psychiatrists and, most days, took his tranquillisers (Largactil), even though they made him put on weight and caused his hands to tremble and shake. He was in and out of the local mental hospital and for one year he was "sectioned" - compulsorily detained. But never again. Seeing her son locked up in hospital, so lost and frightened, not allowed to come home, was too much for Mama to bear.

"Can I ask questions?" was Roger's constant plea. We were told never to agree with any of his delusions, but after 45 minutes of being asked over and over whether there was a windmill in his watch, you sometimes said, if only to make him happier, "Well, if you think so, there could be, but I can't see it." Roger would look triumphant and immediately stop the questioning. But next day he would begin: "You said yesterday, didn't you, that there could be a windmill in my watch ..."

Roger was convinced he had the devil inside him and needed to cough him up. That's why he kept retching and making that terrible noise. He thought he was The One, that he'd been through hell and would now bring us all to heaven. "I made them both," he said. Why weren't we bowing down to him, grateful and thankful?

In his inner world he was a winner, escaping from the reality where he was so obviously, so miserably, a loser.

When Dada, asked the time, replied "3:30, son", Roger went into a fury - he'd meant what time is it in the universe. Fisticuffs and broken ribs would follow. Dada, though a former army boxer, was now in his 60s and no match for Roger's bulk and strength.

Roger would demand that Mama kneel down on the kitchen floor, which she sometimes did, I know, to please him - though not when she thought I was around to be upset. If it made her son happy for a while, what did she care?

When I moved away from home, Roger would sometimes ring my flat two or three times in the middle of the night, just to tell me to fuck off. I would lie there and swear to myself that for Mama's sake I would kill him. But within minutes Roger would call again, this time saying in a shaky voice: "You do love me Carole, don't you?" And of course I did.

One weekend when I came home Mama grabbed my hands and said excitedly: "I've been reading a book [The Divided Self by the psychiatrist R D Laing], which suggests it could be us who are mad and Roger who is sane. It seems it's the family that causes the problem. If we just treat Roger as normal he'll be fine." I ran upstairs to find Roger with his feet on the television watching a film. I offered him a cup of tea which he gruffly accepted. So far, so good. But I must have clattered the cups when I took the tray in, for within seconds Roger was on his feet hurling a chair into the television - which exploded - yelling at me: "Be quiet. Don't you know who I am?"

I walked sadly back down the stairs. "It doesn't work Mama," I said. "It doesn't work."

Laing's legacy lingers: too many families still feel their child's schizophrenia is all their fault. But Laing did write brilliantly about the experience of mental illness. He gave hope to people who had been ignored for far too long. He listened to their pain. He treated them as people. I think Roger would have liked him.

We still don't know what causes schizophrenia. Maybe it's in the genes, perhaps a chemical imbalance that can be triggered by events, stress, tensions within the family.

Mama wrote a book about Roger. It helped her make sense of what had happened to her son - and of the experience of seeing him literally go mad before her eyes. She called it One in a Hundred, because we do know schizophrenia affects about 1% of the population.

Dada, as he grew older, became less and less involved with Roger's problems. He retreated, contentedly enough, from life, and died aged 76. Roger showed no particular emotion at the time, but afterwards always spoke about his father with affection.

Three years later Mama, through an ad she put in the local lonely hearts column, remarried and moved in with her new husband, Ted.

She gave up the newsagent's, and Roger was given his own council bedsitter. He had "argy bargies" with the neighbours or with children who pestered him, but he coped. Mama visited him twice a week. One morning she arrived to find him slumped in the armchair. He had had a stroke. In the bleak hours that followed - it took over four hours for the ambulance to get there - Mama sat talking to her son, holding his hand. She told me she could tell by his eyes that he understood her.

Roger died four days later, a few days short of his 45th birthday. The death certificate gave the immediate cause of death as a "stroke", but then added unnecessarily: "known schizophrenic". That was his illness, but much more importantly he was a son, a brother, a human being known and loved by his family, and especially by his mother.

Mama ended her book with these words: "I have struggled to keep alive in Roger his individuality, his dignity. I have tried to treat him, not as a 'schizophrenic' but to maintain in him the feeling that he is a member of the public."

Eventually, Mama got over Roger's death, but she never got over his life.

· The mental health charity Sane runs a helpline for anyone affected by mental illness on weekdays from noon to 11pm and at weekends from noon to 6pm. Call 0845 767 8000.

· Carole Stone is the author of Networking: the Art of Making Friends (Vermilion)