The study retrospectively evaluated risk factors for osteopenia in anorexia nervosa (AN) patients. Sixty-nine outpatient, female anorexia nervosa patients (age range 20-40 years, mean 27.5) at varying stages of recovery, and 31 controls had lumbar spine trabecular bone density assessed with single energy computed tomography (CT) scans. An investigator-based, semistructured interview assessed weight and menstrual histories from age 10. Current exercise and dietary calcium levels were categorized and lifetime durations in categories were estimated for each subject. Bone density was significantly lower in the patient group (mean 120 mg/cm3) than in the controls (mean 148 mg/cm3, P less than 0.001). Bone density correlated significantly with duration of illness, amenorrhea, and weight histories but not with measures of dietary calcium or exercise histories. The most important predictor of bone loss on stepwise multiple regression analysis was duration of AN (23% of variance, P less than 0.001), and duration of an inadequate calcium intake in adolescence explained a further 5% of the variance (P = 0.052). There was no evidence that regular exercise and adequate dietary calcium prevented bone loss related to prolonged periods of low weight and amenorrhea in these subjects.