BACKGROUND:Previous studies have reported an increased risk ofcataractfor breast cancer patients treated withtamoxifen. We assessed whether breast cancer patients treated withtamoxifenwere at increased risk of developingcataractscompared to women not prescribedtamoxifen.METHODS:We used a nested, matched case-control study design and data collected in the General Practice Research Database. We identified all women 30-79 years old who were diagnosed with breast cancer and treated withtamoxifenwithin 6 months, or with bladder cancer, colorectal cancer or non-melanoma skin cancer between January 1991 and December 1999. From this population, we identified all newly diagnosed cases ofcataract. We matched four female controls to each case on age (+/- 1 year), index date and study entry date (+/- 6 months). We assessed the risk ofcataractsfor current, past and ever users oftamoxifenand according to cumulative use oftamoxifen. We calculated adjusted odds ratios (AOR) and 95% confidence intervals (CI) controlling the matching factors and adjusting for importantcataractrisk factors.FINDINGS:Currenttamoxifenusers were at no increased risk ofcataract(AOR = 1.0, 95% CI: 0.7, 1.4). There was no evidence of an increased risk with increasing cumulative dose.INTERPRETATION:We detected no increased risk ofcataractamong breast cancer patients who were treated withtamoxifencompared to women with other cancers who were not prescribedtamoxifen.