Patterns of hormone replacement therapy (HRT) use over time and predictors of initiating or discontinuing use were examined in a longitudinal study. A cohort of 2,425 women aged 45-55 years identified from a population-based random survey in Massachusetts in 1981-1982 was followed by six telephone interviews, 9 months apart. Cohort participants were either premenopausal (66.8%) or in early perimenopause (33.2%). During the study, prevalence of use was low overall (12.3%) and was considerably higher for surgical menopause (45%) than for peri- (9.3%), natural (4.5%), or premenopause (1.5%). Predictors of HRT uptake and discontinuation (from time t - 1 to time t) were examined by repeated-measures logistic regression, stratified by surgical status. For surgical menopause, the only significant predictor of HRT uptake was recent surgery (odds ratio = 4.4; 95% confidence interval 2.73-7.22), while for nonsurgical subjects, menopausal status (primarily perimenopause), prior use of HRT, health care utilization, hot flashes, alcohol consumption, regular exercise, and leaner body mass were all significant predictors of uptake. Discontinuing HRT was inversely associated with surgical and perimenopause and positively related to prior short-term use and health care utilization. Nonsurgical HRT users had a somewhat more favorable cardiovascular risk profile than did nonusers.