It is unclear whether breast cancer risk varies by age and menopausal status in relation to use of hormonal birth control (HBC) and hormone replacement therapy (HRT), taken singly or cumulatively. The authors utilized data from 1,478 cases and 1,493 controls aged 20-98 years with known menopausal status, who had participated in a population-based, case-control study conducted on Long Island during 1996-1997. Exogenous hormone use over the lifecourse was assessed by use of memory aids. The authors examined associations among women in these subgroups: premenopausal (n = 968), postmenopausal <65 years (n = 1,045), and postmenopausal > or = 65 years (n = 958). Among premenopausal women, risk was increased for ever use of HBC (odds ratio (OR) = 1.37, 95% confidence interval (CI): 1.04, 1.81) or HRT (OR = 1.81, 95% CI: 1.17, 2.81) and was pronounced among women reporting use of both HBC and HRT (OR = 2.59, 95% CI: 1.50, 4.46), long-term HRT use (OR = 3.93, 95% CI: 1.43, 10.84), or estrogen-plus-progestin therapy (OR = 3.51, 95% CI: 1.45, 8.49). There was no effect of ever HBC use among postmenopausal women aged less than 65 years, but risk was modestly elevated for more than 5 years of HRT use (OR = 1.41, 95% CI: 1.00, 1.99). Among postmenopausal women aged 65 years or more, odds ratios for HBC or HRT use were around the null. These results emphasize that timing of exogenous hormone use is important. Women who used these hormones before menopause had elevated risks, but the harmful effects began to decline with age after menopause.