This article looks at the issues of excessive daytime sleepiness and unintended sleep episodes in patients with Parkinson's disease (PD) and explores the reasons why patients might suffer from these symptoms, and what steps could be taken to manage them. During the last decade, understanding of sleep/wake regulation has increased. Several brainstem nuclei and their communication pathways in the ascending arousing system through the hypothalamus and thalamus to the cortex play key roles in sleep disorders. Insomnia is the most common sleep disorder in PD patients, and excessive daytime sleepiness is also common. Excessive daytime sleepiness affects up to 50% of PD patients and a growing body of research has established this sleep disturbance as a marker of preclinical and premotor PD. It is a frequent and highly persistent feature in PD, with multifactorial underlying pathophysiology. Both age and disease-related disturbances of sleep-wake regulation contribute to hypersomnia in PD. Treatment with dopamine agonists alsocontributeto excessive daytime sleepiness. Effective management of sleep disturbances and excessive daytime sleepiness can greatly improve the quality of life for patients with PD.