This study prospectively investigated the course of bone mineral density (BMD) in patients with anorexia nervosa (AN) and bulimia nervosa (BN) over a 3.6-yr follow-up period. From an initial sample of 47 female patients with an eating disorder (T1), 38 (n = 24 AN; n = 14 BN) were reassessed at follow-up (T2) (participation rate, 80.1%). For nonrecovered AN patients at T2, prevalence rates of osteopenia (-1.0 SD > or = T-score > -2.5 SD) and osteoporosis (T-score < or = -2.5 SD) at the lumbar spine were 54.2 and 20.8%, respectively. Due to an annual loss of lumbar spine BMD (-3.7 +/- 4.9%) in the chronic AN patients and a slight but insignificant annual increase (0.7 +/- 1.7%) for those who recovered, the difference in BMD between both outcome groups was more pronounced at follow-up (0.93 +/- 0.13 vs. 1.14 +/- 0.13 g/cm2; P < 0.01). Nonrecovered AN patients with binge eating/purging type showed a significantly reduced BMD compared with patients with the restricting type (0.87 +/- 0.13 vs. 1.02 +/- 0.08 g/cm2; P = 0.02). Both at baseline and follow-up, AN patients had increased rates of bone resorption, as measured by urinary desoxypyridinoline, compared with a control group (n = 42) (11.4 +/- 4.4 vs. 10.4 +/- 7.8, P < 0.001, vs. 5.6 +/- 2.4 and 10.4 +/- 7.8 nM/mM creatinine, P < 0.05, respectively). The subtype of AN and body mass index were best predictors for BMD at the lumbar spine at follow-up (R2 = 0.576). With one exception, all bulimic patients had BMD and markers of bone turnover within the normal range. These results suggest that patients with chronic AN, particularly of the binge eating/purging type, are at high risk for osteoporosis and may need additional therapy to prevent bone loss.