Objective: Despite proven efficacy of cognitive behavioral therapy (CBT) for treating eating disorders with binge eating as the core symptom, few patients receive CBT in clinical practice. Our blended efficacy-effectiveness study sought to evaluate whether a manual-based guided self-help form of CBT (CBT-GSH), delivered in 8 sessions in a health maintenance organization setting over a 12-week period by master's-level interventionists, is more effective than treatment as usual (TAU). Method: In all, 123 individuals (mean age = 37.2; 91.9% female, 96.7% non-Hispanic White) were randomized, including 10.6% with bulimia nervosa (BN), 48% with binge eating disorder (BED), and 41.4% with recurrent binge eating in the absence of BN or BED. Baseline, posttreatment, and 6- and 12-month follow-up data were used in intent-to-treat analyses. Results: At 12-month follow-up, CBT-GSH resulted in greater abstinence from binge eating (64.2%) than TAU (44.6%; number needed to treat = 5), as measured by the Eating Disorder Examination (EDE). Secondary outcomes reflected greater improvements in the CBT-GSH group in dietary restraint (d = 0.30); eating, shape, and weight concern (ds = 0.54, 1.01, 0.49, respectively; measured by the EDE Questionnaire); depression (d = 0.56; Beck Depression Inventory); and social adjustment (d = 0.58; Work and Social Adjustment Scale), but not weight change. Conclusions: CBT-GSH is a viable first-line treatment option for the majority of patients with recurrent binge eating who do not meet diagnostic criteria for BN or anorexia nervosa. (Contains 3 tables and 2 figures.)