Given that weight gain patterns in adolescents receiving outpatient Family-Based Treatment (FBT) have not been characterized, the purpose of this study was to examine trajectories of weight gain in a group of adolescent patients with a restrictive eating disorder [e.g., anorexia nervosa (AN) and atypical AN] receiving FBT. This study also examined the association of patient characteristics with weight gain trajectories, including age, diagnosis, weight suppression, presenting BMI-for-age percentile, and eating pathology.