The authors examined the association between age at menarche, menstrual cycle characteristics between ages 28 and 32 years, and peri- and postmenopausal fracture risk in a cohort of 874 women who prospectively recorded menstrual cycle data for at least 5 years from their early 20s through their menopause. Fracture history was obtained with a self-administered questionnaire. The mean age of respondents at the time the questionnaire was completed was 73 years. Wrist fracture (n = 62) risk increased with increasing age at menarche (odds ratio 3.3, 95% confidence interval 1.7-6.2) for menarche age > or = 14 years compared with 12-13 years) and increasing mean cycle length at age 28-32 (odds ratio 2.2, 95% confidence interval 1.0-4.9) for > 30.5 days compared with 26.6-30.5 days). Similar results were seen in analyses of the combined wrist, hip, or vertebral fracture group (n = 92). These prospectively recorded menstrual diary data indicate that age at menarche and menstrual cycle patterns may have a long-term association with fracture risk, with effects lasting into the postmenopausal years.