I am lying belly up waiting for my obstetrician to stick a big needle into my womb. The decision to have an amniocentesis, to check my baby has no major genetic problems, has not been taken lightly. But will it hurt? "It's not painful," says my obstetrician. "Tomorrow you might feel a slight discomfort." The first part is true, but the next day I feel as though a horse has kicked me in the stomach. Is this a slight discomfort? I don't think so. Seriously worried I'm about to lose the baby, I phone a friend who had an amniocentesis a year ago. "How did you feel the next day?" I ask. The answer is immediately reassuring: "Like someone kicked me in the guts."

Two weeks later I tell my obstetrician about the descriptive gulf. "We're bad at asking women what they felt like after tests," he says. "In research trials, doctors look at miscarriage rates, not at how much pain women felt. So we don't know."

But from today doctors will be able to learn a whole lot more about patients' feelings. A team led by Dr Ann MacPherson from the University of Oxford has set up a website of patients' experiences. The initiative, called Dipex, which stands for a database of individual patient experience, has so far collected the stories of people with prostate cancer and high blood pressure. Those of people with breast, bowel and cervical cancer will be available within the next six months. Other conditions are in the pipeline. On the Dipex website you can watch patients' video evidence, listen to their voices or read their stories. For prostate cancer alone the team collected testimonies from 60 people.

"The database means you get a wide range of experience rather than just one or two stories from patients," says MacPherson. "It's different from a television documentary about an illness that might focus on the most attractive or tragic rather than the full range of stories."

The idea for the website came out of Dr MacPherson's own diagnosis of breast cancer six years ago. "Even though I was a GP and knew something about breast cancer, it was very helpful to talk to people," she says. "When I had chemotherapy, the doctor said, 'Just drop in, have the chemo and then you can go to work.' Well I couldn't do that. I was surprised how ill I felt. Through talking to people I found there was a wide range of experience but only a minority of women who had my chemo could go to work straight afterwards.

"No one knows about these things better than the patient. We hope that doctors and medical students will use Dipex to learn what questions patients have about their illnesses and what it's like to live with a disease. These questions should then inform what research needs to be done to answer them."

Dr Richard Smith, editor of the British Medical Journal, agrees. "Research trials often don't gather evidence on the things that matter to patients. In breast cancer trials the evidence that the drug tamoxifen works is overwhelming. But it can have side effects of which one is that it can seriously alter your voice. Now doctors may think, 'So what, you've got breast cancer.' But if the woman taking it is a singer and her whole quality of life is changed then this really matters to her.

"There's no doubt that doctors and patients think about different sorts of things and have different priorities. It's not malignant unless doctors charge ahead and don't listen to patients. There's a world of difference between being a student of a disease and having that disease. It's like the difference between reading about and having sex. If I got diabetes tomorrow I'd like to hear the patients' perspective."

When Alex McKenzie was diagnosed with prostate cancer a year ago at the age of 50 he not only scoured the internet for information on treatment but also flew to a radiotherapy centre in Georgia Atlanta to talk to doctors and patients. "I was shocked at my diagnosis," he says, "My father had died from prostate cancer and my doctor said if I didn't have treatment I would have a low probability of living to 75. He said there were three different types of treatment; to remove the whole prostate gland, have external radiation or to implant radioactive seeds in the prostate. I wanted to know as much as possible before making my decision. I knew that surgery could leave me incontinent and impotent, although the doctor wasn't that explicit about it."

After investigating the team in Georgia's results, Alex chose to have his treatment there. His story is on the Dipex site. He was happy to participate because of the help he got from other people with his condition. "The prostate cancer charities were very helpful. Men can be less likely to talk about their illness, but I think that's stupid. Only good can come out of talking about it. I still feel emotional when I think of the first time someone said to me, 'I'm so sorry, I know how you must feel.' However good your doctor is you don't always want to talk to someone with a white coat."

Fiona Teddy, whose testimony on breast cancer appears on the site, believes her medical care was excellent but would still have liked to have access to Dipex when she was diagnosed. "You're in such a state of terror," she says. "It was the unknown that was so frightful. I would have been able to face things more easily if I had known more about what treatment involved.

"The doctor doesn't have the experience of having radiotherapy. I felt terribly tired and a bit sick, but it wasn't that bad and it would have helped not to have been unnecessarily alarmed. I was 44 at the time and my first thought was that I wouldn't see my children grow up. Experiences vary but it would have been good to have heard that breast cancer isn't always ghastly. Sometimes it is easier to just listen to someone talking about their experience rather than have to open up yourself and talk to them. The beauty about Dipex is that you can just click on and off."

Dipex (www.dipex.org) will be freely available to everyone. It has charitable status and is funded by the Department of Health and Macmillan Cancer Relief. MacPherson hopes that hospitals, GP surgeries, libraries and cancer information centres will also provide access to the site. "We've been surprised by how open people are when we've interviewed them," says MacPherson. "Maybe people don't usually have the opportunity to discuss how they feel. And you can feel very isolated and alone with an illness."