The study objective was to investigate a possible association between statin use and breast cancer (BRCA). An historical cohort design based on Saskatchewan's population health services databases was used. All eligible women with > or = 1 statin prescription from 1989 to mid-1997 and an age-sex-matched nonexposed group were followed up to 8.5 years (mean 4.2 years). Relative rates (RR) of BRCA were estimated and stratified by age, statin exposure time, and prior hormone use. Thirteen thousand five hundred ninety-two statin users and 53,880 nonexposed subjects were identified. Eight hundred seventy-nine incident BRCA cases were identified. Statins were not associated with BRCA risk in women < or = 55 years. Among subjects >55 years, the RR for BRCA was 1.15 (0.97, 1.37). Stratified analyses revealed increases in risk in short-term statin users and statin users with long-term hormone replacement therapy (HRT) exposure. More studies are needed to determine if short-term statin use and statin use with long-term HRT exposure increases postmenopausal BRCA risk. Published by Elsevier Science Inc.