Recent research has identified the important but overlooked role of negative affect in the maintenance of dietary restriction. However, understanding how fluctuations in negative affect relate to symptoms of anorexia nervosa (AN) during treatment is limited. In a longitudinal study, the reciprocal associations between higher and lower order dimensions of negative affect and dietary restraint were examined in adolescents undergoing treatment for AN. The sample consisted of 107 adolescents (Mage = 15.5, SD = 1.5 years) who underwent family-based treatment over the course of 6 months. Self-report data assessing negative affect and dietary restraint were collected at baseline, 6 times throughout treatment, and again at the end of treatment. Findings from lagged hierarchical linear models revealed reciprocal associations between higher order negative affect and dietary restraint but unidirectional associations among some dimensions of lower order affect. Specifically, dietary restraint predicted increased guilt and hostility, whereas fear predicted increased dietary restraint. These findings highlight the importance of examining the distinct dimensions of negative emotion and the temporal role of fear in precipitating dietary restraint, and guilt and hostility in proceeding dietary restraint. Collectively, these findings emphasize the functional nature of different emotions in the process of AN remission and provide preliminary evidence of affective mechanisms related to change in symptomatology during treatment for adolescent AN. (PsycINFO Database Record (c) 2019 APA, all rights reserved).