This 3-year follow-up compared insomnia treatment to depression treatment for patients with both diagnoses. Forty-three participants were randomized to either treatment, in the form of Internet-delivered therapist-guided cognitive behavior therapy (CBT), and 37 (86%) participants provided primary outcome data at the 3-year follow-up. After 3 years, reductions on depression severity were similar in both groups (between-group effect size, d = 0.33, p = .45), while the insomnia treatment had superior effects on insomnia severity (d = 0.66, p < .05). Overall, insomnia treatment was thus more beneficial than depression treatment. The implication for practitioners, supported by previous research, is that patients with co-occurring depression and insomnia should be offered CBT for insomnia, in addition to medication or psychological treatment for depression.