The present study examined pretreatment and process predictors of individual nonresponse to psychological group treatment of binge eating disorder (BED). In a randomized trial, 162 overweight patients with BED were treated with either group cognitive-behavioral therapy or group interpersonal psychotherapy. Treatment nonresponse, which was defined as nonabstinence from binge eating, was assessed at posttreatment and at 1 year following treatment completion. Using 4 signal detection analyses, greater extent of interpersonal problems prior to treatment or at midtreatment were identified as predictors of nonresponse, both at posttreatment and at 1-year follow-up. Greater pretreatment and midtreatment concerns about shape and weight, among those patients with low interpersonal problems, were predictive of posttreatment nonresponse. Lower group cohesion during the early treatment phase predicted nonresponse at 1-year follow-up. Attention to specific pre- or intreatment predictors could allow for targeted selection into differential or augmented care and could thus improve response to group psychotherapy for BED.