Purpose: Persistent insomnia is a common complaint in cancer survivors, but is seldom satisfactorily addressed. The adaptation to cancer care of a validated, cost-effective intervention may offer a practicable solution. The aim of this study was to investigate the clinical effectiveness of protocol-driven cognitive behavior therapy (CBT) for insomnia, delivered by oncology nurses. Patients and Methods: Randomized, controlled, pragmatic, two-center trial of CBT versus treatment as usual (TAU) in 150 patients (103 females; mean age, 61 years.) who had completed active therapy for breast, prostate, colorectal, or gynecological cancer. The study conformed to CONSORT guidelines. Primary outcomes were sleep diary measures at baseline, post-treatment, and 6-month follow-up. Actigraphic sleep, health-related quality of life (QOL), psychopathology, and fatigue were secondary measures. CBT comprised five, small group sessions across consecutive weeks, after a manualized protocol. TAU represented normal clinical practice; the appropriate control for a clinical effectiveness study. Results: CBT was associated with mean reductions in wakefulness of 55 minutes per night compared with no change in TAU. These outcomes were sustained 6 months after treatment. Standardized relative effect sizes were large for complaints of difficulty initiating sleep, waking from sleep during the night, and for sleep efficiency (percentage of time in bed spent asleep). CBT was associated with moderate to large effect sizes for five of seven QOL outcomes, including significant reduction in daytime fatigue. There was no significant interaction effect between any of these outcomes and baseline demographic, clinical, or sleep characteristics. Conclusion: CBT for insomnia may be both clinically effective and feasible to deliver in real world practice.