Adolescence is a common period for eating disorder (ED) onset. The availability of psychometrically sound measures of ED psychopathology enables clinicians to accurately assess symptoms and monitor treatment outcomes continuously from adolescence and adulthood. The purpose of this study was to assess if the Eating Pathology Symptoms Inventory (EPSI) is invariant across adolescents and adults. Participants (N = 29,821) were adolescent (n = 5250) and adult (n = 24,571) users of the Recovery Record (RR) mobile phone application who provided EPSI responses through the application. Measurement invariance testing was conducted to assess invariance of the EPSI Body Dissatisfaction, Restricting, Excessive Exercise, Purging, Cognitive Restraint, and Binge Eating scales across adolescents (age 13 through 17) and adults (age 18 and older). Findings indicated that all EPSI factors administered in the RR app replicated in both adolescent and adult users. The EPSI factor structure was largely equivalent in adolescents and adults, demonstrating evidence for configural and metric invariance, as well as some evidence for scalar invariance. Our results indicated that EPSI scales measured the same constructs across development. Clinicians and researchers may benefit from utilizing the EPSI to measure ED psychopathology in adolescents and for continued progress monitoring into adulthood.