BACKGROUND: Identifying distinct trajectories of change in body weight during inpatient treatment for anorexia nervosa (AN) may provide knowledge about the process of weight restoration and may help detect optimal body weight response patterns among individuals who are at risk for not achieving weight restoration or leaving treatment prematurely. OBJECTIVE: This study explored the extent to which distinct trajectories of change in body weight existed among individuals during inpatient treatment for AN. DESIGN: Group-based trajectory modeling was used to identify distinct trajectories of change in body weight among 500 individuals receiving inpatient treatment for AN. RESULTS: Four distinct trajectories were identified: weight gain (n = 197), treatment resistant (n = 177), weight plateau (n = 82), and weight fluctuate (n = 44). CONCLUSION: Clinically, it is important to consider the heterogeneity of changes in body weight during inpatient treatment to help guide interventions and outcomes.