Cognitive behavioral therapy-based guided self-help (CBT-GSH) via the Internet has been shown to be effective in the treatment of bulimia nervosa (BN) and similar eating disorders (EDs), but it is rarely offered, and little is known about the effects, in clinical settings. The present study investigated the effects of a bibliotherapy-based CBT-GSH with Internet support in a clinical setting. Participants were 48 adult outpatients who were recruited without randomization from a specialized ED clinic, diagnosed with BN or similar eating disorder. Forty-eight patients in an intensive day patient program (DPP) were used as comparison group. The Eating Disorder Examination Questionnaire (EDE-Q) and the Eating Disorder Inventory 2 measured pre- and post treatment symptoms. Results showed that both groups attained significant improvements in core- as well as related ED symptoms in both instruments. As expected, treatment effects were larger in the more intensive DPP. Nonetheless, bibliotherapy CBT-GSH appears to be a cost-effective treatment that represents a new way to provide more CBT in clinical settings.