Parkinson's disease (PD) is a degenerative disorder of the central nervous system and more common in the elderly, with most cases occurring after the age of 50. The motor symptoms of PD result from the death of dopamine-generating cells in the substantia nigra, a region of the midbrain; the cause of this cell death is unknown. Early in the course of the disease, the most obvious symptoms are movement-related; these include shaking, rigidity, slowness of movement and difficulty with walking and gait. Nonmotor symptoms (NMS) are very common in PD and may result in significant disability. Several studies have shown that n NMS, such as depression, anxiety and apathy, psychosis (e.g., hallucinations, delusions), sleep disturbance, and pain may have a greater adverse impact on quality of life and health economics compared with motor symptoms. Non-motor symptoms can be divided into four domains: neuropsychiatric (e.g., depression, anxiety, apathy, hallucinations, dementia), autonomic (e.g., constipation, orthostatic hypotension, urinary changes, sweating abnormalities), sleep (e.g., insomnia, sleep fragmentation, excessive daytime sleepiness, rapid eye movement, sleep behavioural disorder, restless leg syndrome), and sensory dysfunction (e.g., pain, olfactory dysfunction). This lecture addresses diagnosis and treatment of these disorders. The diagnosis is often challenging, especially for psychiatric disorders, and in particular affective disorders, because somatic features of psychopathology may overlap with the movement disorder itself. Treatments used are limited and psychiatric drugs may not be as effective as in general population.