ObjectiveTo test the efficacy of cogntive‐behavioral therapy for insomnia (CBT‐I) as a supplement treatment for psychiatric outpatients. Comorbid insomnia is prevalent among individuals with varied psychiatric disorders and evidence indicates that CBT‐I may be effective for reducing insomnia and other psychiatric symptoms. Method The present study randomly assigned 30 psychiatric outpatients (mean duration of treatment = 3.6 years) with low sleep quality and residual depressive symptoms to two sessions of CBT‐I or a treatment as usual control group. Assessment included the Pittsburgh Sleep Quality Index (PSQI) for insomnia and the Patient Health Questionnaire (PHQ‐9) for depression at pretreatment and 4 and 8 weeks posttreatment. Results Patients who received CBT‐I demonstrated within group changes in PSQI and the PHQ‐9 scores at both 4 and 8 weeks posttreatment, but did not show between‐group differences. Additionally, 38% of the treatment participants achieved normal sleep at follow‐up compared with none in the control condition. Conclusions This study provides preliminary evidence that abbreviated behavioral treatment has beneficial effects on residual insomnia and depression in long‐term psychiatric outpatients.