Abstract Psychiatric symptoms are important non-motor features in PD, which occur at high frequency and have significant impact on health related quality of life. This review concentrates on the prevalence, pathophysiology, diagnosis and treatment of depression, anxiety, apathy and psychosis. The pathophysiology of these disorders is complex, reflecting the widespread brainstem and cortical pathology in PD, with involvement of several neurotransmitters, including dopaminergic, serotonergic, noradrenergic and cholinergic systems. The diagnosis of psychiatric conditions, in particular affective disorders, is challenging because of the overlap of somatic features of psychiatric disorders and underlying movement disorder. The pathogenesis is likely to differ considerably from non-PD patients, and treatments used in general psychiatry services may not be as effective in PD and will require clearer clarification in well-designed clinical studies. Management strategies include adjustment of dopaminergic medication, use of psychotropic treatments and behavioural and psychological approaches. However, the future challenge will be to develop treatments developed specifically for the pathogenesis of these disorders in PD.