Sleep disorders are perhaps the commonest non-motor symptom in patients with Parkinson’s disease (PD) and a defining feature of PD. Disorders include insomnia, hypersomnia, parasomnia, visual hallucinations and intense or vivid dreams. Growing evidence indicates that sleep disorders can precede the onset of PD, and a recent study suggested that excessive daytime sleepiness is a risk factor for PD onset. Complications arising from medication may exacerbate sleep disturbances, and sleep disturbances may also contribute to both cognitive and neuropsychiatric disorders.