This study described sleep in a heterogeneous sample of breast cancer patients using the Pittsburgh Sleep Quality Index (PSQI) and examined the relation between sleep disturbance and health-related quality of life as measured by the Rand 36-Item Health Survey. Chemotherapy and radiation therapy were explored as predictors of sleep disturbance in breast cancer patients, and the sleep characteristics of breast cancer patients were compared to the sleep characteristics of a sample of medical patients with general medical conditions. Results showed that 61% of breast cancer patients had significant sleep problems. Sleep was characterized by reduced total sleep time with sleep frequently being disturbed by pain, nocturia, feeling too hot, and coughing or snoring loudly. Despite the frequency of significant sleep disturbance, pharmacological and cognitive-behavioral treatments of sleep problems were observed to be inadequate. Limited evidence was found for the role of chemotherapy and radiation therapy in the sleep disturbance of breast cancer patients, and the general pattern of sleep disturbance in breast cancer patients was not significantly different than that observed in medical patients with general medical conditions. Breast cancer patients having significant sleep problems had greater deficits in many areas of health-related quality of life. The implications of the findings and study limitations are discussed.