Assessment of drug-induced movement disorders was carried out regularly on 104 psychiatric patients requiring antipsychotic medication on admission to hospital. The data relevant to motor restlessness were subjected to a principal components' analysis. According to their component scores, patients were then classified into two main groups: an akathisia group and an illness-related-movement group, the former group showing the clinical and pharmacological characteristics expected of akathisia. Clinical features which distinguished between the two groups, and between grades of akathisia severity, were identified, so an objective, phenomenological description of the akathisia syndrome was possible. Our observations suggested two distinct types of acute akathisia; one related to severe parkinsonism and one not. The implications of these findings are discussed.