OBJECTIVE: Cancer and its treatments disturb sleep-wake functioning; however, there is little information available on the characteristics and consequences of sleep problems associated with cancer. As part of an effort to improve measurement of sleep-wake functioning, we explored the scope of difficulties with sleep in a diverse group of patients diagnosed with cancer. METHODS: We conducted 10 focus groups with patients recruited from the Duke University tumor registry and oncology/hematology clinics. Separate groups were held with patients scheduled to begin or currently undergoing treatment for breast, prostate, lung, colorectal, hematological, and other cancer types and with patients who were in posttreatment follow-up. The content of the focus group discussions was transcribed and analyzed for major themes by independent coders. RESULTS: Participants not only reported causes of sleep disturbance common in other populations, such as pain and restless legs, but they also reported causes that may be unique to cancer populations, including abnormal dreams, anxiety about cancer diagnosis and recurrence, night sweats, and problems with sleep positioning. Many participants felt that sleep problems reduced their productivity, concentration, social interactions, and overall quality of life. Many also shared beliefs about the increased importance of sleep when fighting cancer. CONCLUSIONS: The findings underscore the need for interventions that minimize the negative impact of cancer and its treatments on sleep. This study will inform efforts now underway to develop a patient-reported measure of sleep-wake functioning that reflects the breadth of concepts considered important by patients with cancer.