The authors investigated the risk for breast cancer in schizophrenia in a cohort of 1336313 Danish women born after 1935, including information on reproductive factors. In all, 7541 had been hospitalized for schizophrenia in 1970-1997 and the overall relative risk for breast cancer adjusted for age, period, age at first birth and number of births was not increased (RR, 0.91; 95% confidence interval, 0.71-1.12). Studies not taking parity into account may overestimate the risk for breast cancer in schizophrenic women.