Depression is one of the most common health problems worldwide but is often undertreated. Internet-delivered cognitive behavioral therapy (ICBT) appears to be an effective treatment option, with the potential to reach a larger proportion of individuals suffering from depression. While many studies have examined the efficacy of ICBT for depression in randomized controlled trials, fewer have focused on the effectiveness of ICBT when used as an integral part of routine health care. In this study the effectiveness of an 8-week ICBT program was examined when delivered in a routine psychiatric setting. A total of 108 patients were referred and 54 were then included and randomized to either ICBT or a waitlist control condition. The sample had a lower education level and a higher proportion of individuals were on sick leave than comparable previous efficacy trials of ICBT for depression conducted in Sweden. Measures assessing depression, anxiety and psychiatric symptoms were administered before and after treatment, follow up was performed at 6- and 12 months after treatment had ended. ICBT resulted in significant reductions of depressive symptoms in the treatment group when compared to a waitlist control group with a large effect size (Cohen's d = 1.6). Treatment gains were maintained at 6- and 12 months after the treatment had ended. In terms of clinical significance, 58% of the sample had improved or recovered after treatment. The study was small, and patients received general psychiatric care after the ICBT treatment had ended which limits the implications. We conclude that ICBT appears to be an effective treatment for depression when delivered as an integral part of routine psychiatric care.