This study investigated the efficacy of a multimodal cognitive-behavioral intervention for women who had been treated for nonmetastatic breast cancer. Ten participants were enrolled in the treatment protocol in a multiple-baseline design. Intervention time series analyses of daily sleep diary data revealed significant improvements of sleep efficiency and total wake time. These results were corroborated by polysomnographic data. In addition, insomnia treatment was associated with significant improvements of mood, general and physical fatigue, and global and cognitive dimensions of quality of life. These findings suggest that cognitive-behavioral therapy, previously found effective for primary insomnia, is also of clinical benefit for insomnia secondary to cancer.