Proposed treatments for severe and enduring anorexia nervosa (SE-AN) focus on quality of life, and psychological and social functioning. By de-emphasizing weight restoration as a priority, however, premature diagnosis of SE-AN may reduce potential for recovery. The present study assessed the effect of weight restoration, illness duration, and severity on treatment outcome 6 months after discharge from an intensive, meal-based behavioral treatment program. Participants included hospitalized adult women ( = 191) with AN or underweight other specified feeding and eating disorder (OSFED). Participants were characterized as short-term (ill <7 years; = 74) or long-term ill (ill ≥ 7 years; = 117). Compared with short-term ill, long-term ill patients were older, had lower lifetime body mass index (BMI), more prior admissions, and exhibited greater depression and neuroticism. Long-term vs. short-term ill patients gained weight at the same rate (~2 kg/wk) and were equally likely to be weight restored by discharge (>75% reached BMI ≥ 19 kg/m in both groups). At 6-month follow-up ( = 99), both groups had equivalent self-reported BMI, and depression, drive for thinness, body dissatisfaction, and bulimia scores. The only predictor of BMI ≥ 19 kg/m at follow-up was discharge BMI. The likelihood of a BMI ≥ 19 kg/m at follow-up was 5-fold higher for those with discharge BMI ≥ 19 kg/m. Few studies of long-term ill inpatients with AN have examined the impact of full weight restoration on short-term outcomes. This study supports the therapeutically optimistic stance that, regardless of illness duration, hospitalized patients with AN benefit from gaining weight to a BMI ≥ 19 kg/m.