The object of this study was to examine the effectiveness of an Internet-based therapy (IBT) for bulimia nervosa (BN) as compared to a waiting list (WL). Sixty-two female BN patients, diagnosed according to DSM-IV criteria, were assigned to either the IBT or a WL. The control participants (WL) were matched to the IBT group in terms of age, duration of the disorder, number of previous treatments, and severity of the disorder. Assessment measures included the EDI, SCL-90-R, BITE, the TCI-R, and other clinical and psychopathological indices, which were administrated before and after the treatment. Considering the IBT, while the mean scores were lower at the end of the treatment for some EDI scales (bulimic, interpersonal distrust, maturity fears, and total score) and the BITE symptomatology subscale, the mean BMI was higher at posttherapy. Predictors of good IBT outcome were higher scores on the EDI perfectionism scale and EAT and a higher minimum BMI. Drop-out (after IBT 35.5% of cases) was related to higher SCL-anxiety scores, a lower hyperactivity, a lower minimum BMI, and lower TCI-reward dependence scores. At the end of the treatment, bingeing and vomiting abstinence rates differed significantly between the two groups. Results suggest that an online self-help approach appears to be a valid treatment option for BN when compared to a WL control group, especially for people who present a lower severity of their eating disorder (ED) symptomatology and some specific personality traits. © 2009 Mary Ann Liebert, Inc.