We evaluated the impact of personality on weight restoration in 211 underweight (BMI ≤ 19 kg/m2) females admitted to an inpatient-partial hospitalization program for eating disorders. Symptomatology and personality were assessed by questionnaires, and clinical and demographic variables were assessed by chart review. Neuroticism, a personality trait associated with reactivity to stress, was correlated with higher symptomatology, chronicity, length of stay, and income source. Contrary to our hypothesis, neuroticism was positively associated with weight restoration. Length of stay mediated this relationship such that longer length of stay in patients with high neuroticism explained their higher likelihood of weight restoration prior to program discharge. Higher neuroticism is therefore associated with better weight restoration outcomes but may also indicate greater difficulty transitioning out of intensive treatment.