Binge-eating disorder (BED) is a prevalent health condition associated with obesity. Few people with BED receive appropriate treatment. Personal barriers include shame, fear of stigma, geographic distance to mental health services, and long wait-lists. The aims of this study were to examine the efficacy of an Internet-based cognitive-behavioral intervention for adults with threshold BED (DSM-IV) and to examine the stability of treatment effects over 12 months. Participants were randomly assigned to a 16-week Internet-based cognitive-behavioral intervention (n = 69) or a wait-list condition (n = 70). Binge-eating frequency and eating disorder psychopathology were measured with the Eating Disorder Examination–Questionnaire and the Eating Disorder Examination administered over the telephone. Additionally, body weight and body mass index, depression, and anxiety were assessed before and immediately after treatment. Three-, 6-, and 12-month follow-up data were recorded in the treatment group. Immediately after the treatment the number of binge-eating episodes showed significant improvement (d = 1.02, between group) in the treatment group relative to the wait-list condition. The treatment group had also significantly reduced symptoms of all eating psychopathology outcomes relative to the wait-list condition (0.82 ≤ d ≤ 1.11). In the treatment group significant improvement was still observed for all measures 1 year after the intervention relative to pretreatment levels. The Internet-based intervention proved to be efficacious, significantly reducing the number of binge-eating episodes and eating disorder pathology long term. Low-threshold e-health interventions should be further evaluated to improve treatment access for patients suffering from BED.