['Cognitive-behavioral therapy can effectively treat insomnia (CBT-I). Randomized controlled trials have shown efficacy of self-help CBT-I, but unclear is whether excluding depressive patients boosted treatment effects.', 'We administered unsupported self-help CBT-I to insomnia patients with low and high depression levels. Based on the validated Centre of Epidemiological Studies-Depression (CES-D) scale, the internet-recruited sample (N = 479) was divided into three groups: low depression scores (n\xa0= 198), mild depression scores (n\xa0= 182), and high depression scores (n\xa0= 99). Follow-ups were 4 and 18 weeks after completion of the treatment.', 'At 4-week follow-up, all groups had a similar amelioration on the primary sleep measures (d\xa0= 0.1-0.7; P < 0.05) and the secondary insomnia ratings (d\xa0= 1.2; P < 0.001). The only difference was that the high/mild depression groups had a steeper reduction in depression (d\xa0= 1.0-1.1; P < 0.001) and anxiety scores (d\xa0= 0.7-0.8; P < 0.001) than the low depression group (depression and anxiety: d\xa0= 0.3; P < 0.01), possibly due to floor effects in the latter group. The observed effects were sustained at the 18-week follow-up.'] Do baseline depression levels affect efficacy of cognitive-behavioral self-help treatment for insomnia?