OBJECTIVE: The relevance of repeated body mass index (BMI) assessments for long-term outcome in anorexia nervosa (AN) was studied. METHOD: Two-hundred and twelve adolescent patients aged 10-18 (Mean 14.9) years from five sites were followed up for an average of 8.3 years after first admission. Various predictors of BMI at follow-up were analyzed. RESULTS: In comparison to subjects with normal BMI (>17.5) at final follow-up, subjects with BMI <17.5 had significantly lower age-adjusted BMI prior to onset of the disorder and at discharge from first admission. In addition, all outcome scores indicated poorer functioning in the group with BMI < 17.5. The BMI prior to onset of AN, the BMI at first hospital admission and discharge, and the BMI at final follow up were significantly correlated across time. Higher BMI prior to onset of AN, higher BMI at first discharge, and lower age at first admission predicted a normal BMI (>17.5) at follow-up in a model of logistic regression. CONCLUSION: The long-term outcome of adolescent AN reflects the normal tracking of BMI over time. Presumably, the tracking in AN patients is somewhat reduced in comparison to healthy subjects.