BACKGROUND: Body dysmorphic disorder (BDD) is an often chronic and impairing psychiatric condition. Research shows that smartphone-delivered cognitive behavior therapy (CBT) with coaching may be a scalable and effective treatment for BDD. However, evidence for long-term gain maintenance is limited. OBJECTIVES: The aim of the current study was to examine the long-term outcomes of a smartphone-based CBT for BDD. METHOD: Adults with a primary diagnosis of BDD who completed a 12-week course of smartphone-delivered CBT with coach support were evaluated 3- and 12-months posttreatment. Symptom severity, remission and responder status were assessed with the clinician-rated Yale-Brown Obsessive-Compulsive Scale modified for BDD (BDD-YBOCS). Secondary outcomes were also evaluated and included BDD-related insight, depression, functioning and quality of life. Data were analyzed using four different approaches to missing data, with maximum likelihood estimation as the main approach. RESULTS: There was significant attrition from posttreatment ( CONCLUSIONS: Improvements after coach-supported smartphone-based CBT for BDD are maintained one year after treatment.