BACKGROUND: There is concern about the long-term health impact of ovarian stimulation treatment for infertility, in particular the effect on cancer risk. The aim of this study was to investigate the incidence of cancer in a cohort of women attending a large infertility clinic in the UK. METHODS: Women who were UK residents attending the clinic between January 1, 1975 and December 31, 1989 were identified for the study. The cohort was followed-up and cancer incidence rates calculated. RESULTS: The study cohort was made up of 5556 women of whom 75% had received ovarian stimulation drug treatment at the clinic. A total of 118 cancers (including 55 breast, four corpus uteri and six ovarian) were incident in the cohort from the beginning of 1990 to the end of 1997. The incidence rates of cancer of the breast, corpus uteri and ovary were not significantly different from expectation based on national cancer rates, and were similar for women who had received hormonal treatment to stimulate their ovaries and those who had not. CONCLUSIONS: These data do not support a hypothesis linking infertility treatment involving ovarian stimulation with increased breast, uterine and ovarian cancer over the follow-up period studied.