BACKGROUND: Self-tests that people can do without a health professional are widely available, but there is little information about how many people have used one. Our aim was to describe the prevalence of use. METHODS: An initial questionnaire, sent to 8048 adults registered with six general practices in North Birmingham and Warwickshire and Worcestershire, asked whether the person had self-tested. A second questionnaire validated the use for people from the final four practices by asking how each self-test had been obtained and why it had been used. RESULTS: The age-standardised prevalence of confirmed use for any self-test other than for pregnancy or high blood pressure was 47 (95% confidence interval (CI): 37-57) per 1000 women and 22 (95% CI: 14-30) per 1000 men. If everyone who initially reported use but did not return an eligible second questionnaire had the same rates of confirmed use as eligible responders, this would increase to 95 (95% CI: 81-110) per 1000 women and 55 (95% CI: 41-68) per 1000 men. CONCLUSION: An appreciable minority of the population have self-tested for medical conditions.