It is a hypochondriac's dream come true. Harvard, the Ivy League seat of learning and alma mater of America's rich and powerful, is now offering some education with a difference: a website which can calculate your risk of suffering a major health problem such as a stroke or cancer.

Users who want to know what their chances are of contracting particular forms of cancer or diabetes can click on to the site and get a readout within three minutes after answering a series of questions about their health.

The site's organisers say it attracts more than 1,000 visitors a day, and they are translating it into French and Spanish because of the growing number of users. Initially the site offered a risk assessment for cancer, but last week it expanded to give a similar readout on strokes, heart disease, diabetes and osteoporosis.

The Harvard Centre for Cancer Prevention, part of the university's school for public health, said its site was justified because it allowed it to deliver personalised health messages to those who filled in questionnaires. For example, someone at higher-than-average risk of breast cancer might be told to drink less, or to eat at least three portions of green vegetables a day.

Dr Graham Colditz, the centre's director, said: 'The website pulls all these important diseases into one place and offers consistent, practical prevention messages for each. As you click through the site, you see the far-reaching benefits of a healthy lifestyle and can see that a single risk factor will pack the risk of many different diseases. We hope it will inspire people to make healthy behaviour changes.'

Users fill in a brief questionnaire and then get a description of their risk in the form of a coloured bar graph, which will compare them to men and women of their age. It does not put the risk in percentage terms, but describes it as above or below average, with seven levels of risk.

The site, YourDiseaseRisk.com, also explains how each individual score is calculated. For example, a woman will be at higher risk of diabetes if she is of Asian origin, is overweight and is not taking enough exercise.

A man can lower his risk of colon cancer by taking a multivitamin each day, by reducing the amount of red meat he eats and by cutting down alcohol to less than one unit a day. If he is tall, he is also at greater risk of contracting the disease.

Each question on the site is related to a number that represents the strength of the association between the risk factor and the disease. As you answer questions, the numbers are multiplied to equal your personal risk based on the risk factors that apply to you. The site then compares your risk to the average risk for a person of your age and sex.

British doctors are worried about the popularity of self-screening websites, but if done properly they can be very useful, says John Chisholm of the British Medical Association. 'We have to be open-minded about developments like this. Men are far less likely to go to the doctor for advice than women, and yet they might be far more willing to find out about their health through the privacy of their computer.'

There is growing evidence that more and more people are going to websites for advice, because the interactive approach seems to 'resonate with people', as Colditz puts it. He says people switching to a healthier lifestyle could prevent more than 80 per cent of heart disease and diabetes, 70 per cent of strokes and around half of all cancers.

A disclaimer makes it clear that the advice is just that, advice. 'It does not take the place of regular medical check-ups.'