Objective: To describe the prevalence of self-weighing in the transition period from adolescence to young adulthood and examine cross-sectional and longitudinal associations between self-weighing and weight status, psychological, and behavioral outcomes. Design: Project Eating and Activity in Teens and Young Adults, a longitudinal cohort study that assessed variables 3 times over 10 years. Participants: A total of 1,868 adolescents and young adults. Main Outcome Measures: Weight, body mass index, weight disparity, body satisfaction, weight concern, self-esteem, depression, and unhealthy weight control behaviors. Analysis: Cross-sectional and longitudinal. Results: Significant positive correlations were found at each time point between self-weighing and weight concern for both genders. Self-weighing was significantly inversely related to self-esteem at each time point in female participants. Increases in endorsement of self-weighing were significantly related to decreases in body satisfaction and self-esteem and increases in weight concern and depression in female participants and to increases in weight concern in male participants. Conclusions and Implications: Findings suggest that self-weighing may not be an innocuous behavior for young people, particularly women. Interventions should assess potential harmful consequences of self-weighing in addition to any potential benefits. It may be appropriate for clinicians to ask about self-weighing, and if it is frequent, to explore motivations, perceived benefits, and potential adverse correlates or consequences.