Internet-delivered self-help for depression with therapist guidance has shown efficacy in several trials. Results from meta-analyses suggest that guidance is important and that self-help programs without support are less effective. However, there are no direct experimental comparisons between guided and unguided internet-based treatments for depression. The present study compared the benefits of a 10-week web-based unguided self-help treatment with the same intervention complemented with weekly therapist support via e-mail. A waiting-list control group was also included. Seventy-six individuals meeting the diagnostic criteria of major depression or dysthymia were randomly assigned to one of the three conditions. The Beck Depression Inventory (BDI-II) was used as the primary outcome measure. Secondary outcomes included general psychopathology, interpersonal problems, and quality of life. Sixty-nine participants (91%) completed the assessment at posttreatment and 59 (78%) at 6-month follow-up. Results showed significant symptom reductions in both treatment groups compared to the waiting-list control group. At posttreatment, between-group effect sizes on the BDI-II were d = .66 for unguided self-help versus waiting-list and d = 1.14 for guided self-help versus waiting-list controls. In the comparison of the two active treatments, small-to-moderate, but not statistically significant effects in favor of the guided condition were found on all measured dimensions. In both groups, treatment gains were maintained at 6-month follow-up. The findings provide evidence that internet-delivered treatments for depression can be effective whether support is added or not. However, all participants were interviewed in a structured diagnostic telephone interview before inclusion, which prohibits conclusions regarding unguided treatments that are without any human contact.