This article examines the epidemiological data on chronic akathisia, tardive akathisia, and withdrawal akathisia. The limitations of the data are discussed--in particular, the lack of consistent definitions of the syndromes. The studies suggest that a significant proportion of patients chronically treated with neuroleptics suffer from akathisia. The prevalence may be as high as 40 percent, although a conservative estimate would be closer to 30 percent. Risk factors for the development of chronic akathisia and tardive akathisia are poorly understood, but old age, female sex, iron deficiency, negative symptoms, cognitive dysfunction, and affective disorder diagnosis need to be studied further for their potential role. While there is convincing evidence that akathisia may develop after neuroleptic cessation or reduction in dose, the prevalence and risk factors for withdrawal akathisia are not known. Reports of akathisia in children and the elderly have been few, and more systematic research is necessary. Akathisia appears to be common in individuals with mental retardation treated chronically with neuroleptics.