The authors examined rapid response in 75 overweight patients with binge eating disorder (BED) who participated in a randomized clinical trial of guided self-help treatments (cognitive-behavioral therapy [CBTgsh] and behavioral weight loss [BWLgsh]). Rapid response, defined as a 65% or greater reduction in binge eating by the 4th treatment week, occurred in 62% of CBTgsh and 47% of BWLgsh participants. Rapid response was unrelated to most patient characteristics except for eating psychopathology and depressive symptoms. Participants with rapid response were more likely to achieve binge remission and had greater improvements in overall eating pathology and depressive symptomatology than participants without rapid response. Rapid response had different prognostic significance for the 2 treatments. In terms of binge eating, participants receiving CBTgsh, but not BWLgsh, did equally well regardless of whether they experienced rapid response. In terms of increasing restraint and weight loss, participants with rapid response receiving BWLgsh had greater restraint and weight loss than participants receiving CBTgsh. Rapid response has utility for predicting outcomes, provides evidence for specificity of treatment effects, and has implications for stepped care treatment models of BED.