Insomnia affects up to 50% of patients with cancer, but has received little attention from the oncology community compared with other symptoms such as pain and fatigue. Insomnia and subsequent sleep disturbances can lead to fatigue, mood disturbances, and contribute to immunosuppression, which can have a profound impact on quality of life and perhaps affect the course of disease. Insomnia in cancer patients must be distinguished from cancer-related fatigue. Although they are 2 distinct conditions, insomnia and fatigue are interrelated. Insomnia often leads to daytime fatigue that interferes with normal functioning. Conversely, daytime fatigue can lead to behaviors such as napping, which result in insomnia. The primary goal of insomnia treatment should first be to relieve any underlying disorder (eg, cancer pain, depression, anxiety) that may be causing the sleep disturbance. Because insomnia in this patient population may be due to a variety of causes, treatment must be multimodal and include both pharmacologic and nonpharmacologic therapies. A plan that combines attention to sleep hygiene and cognitive-behavioral therapy with prescription of hypnotic medications can help relieve the symptoms of insomnia in cancer patients and improve their quality of life.