On the basis of a literature review it is concluded that mass hysteria can be divided into two syndromes. One form, to be called 'mass anxiety hysteria', consists of episodes of acute anxiety, occurring mainly in schoolchildren. Prior tension is absent and the rapid spread is by visual contact. Treatment consists of separating the participants and the prognosis is good. The second form, to be called 'mass motor hysteria', consists of abnormalities in motor behaviour. It occurs in any age group and prior tension is present. Initial cases can be identified and the spread is gradual. Treatment should be directed towards the underlying stressors but the outbreak may be prolonged. In mass anxiety hysteria the abnormality is confined to group interactions; in mass motor hysteria abnormal personalities and environments are implicated.