Cognitive-behavioral interventions are the most extensively researched form of psychological treatment and are increasingly offered through the Internet. Internet-based interventions may save therapist time, reduce waiting-lists, cut traveling time, and reach populations with health problems who can not easily access other more traditional forms of treatments. We conducted a systematic review of twelve randomized controlled or comparative trials. Studies were identified through systematic searches in major bibliographical databases. Three studies focused on patients suffering from pain, three on headache, and six on other health problems. The effects found for Internet interventions targeting pain were comparable to the effects found for face-to-face treatments, and the same was true for interventions aimed at headache. The other interventions also showed some effects, although effects differed across target conditions. Internet-delivered cognitive-behavioral interventions are a promising addition and complement to existing treatments. The Internet will most likely assume a major role in the future delivery of cognitive-behavioral interventions to patients with health problems.