Involuntary movements originate from different parts of the nervous system. The character of movements depends upon the site of the lesion and the type of pathological change. The presence of more than one type of involuntary movement in a patient can cause confusion and difficulty in the proper classification of movement disorders, which then leads to problems in the differential diagnosis and appropriate treatment. This work was planned to estimate the prevalence and to study the aetiological factors of chorea, dystonia, athetosis and hemiballismus in Assiut, a representative community of Upper Egypt. This study was carried out on 7,000 families (42,000 subjects) representing different types of communities (2,000 families from urban, 2,000 families from suburban and 3,000 families from rural communities). All members of these samples were personally interviewed at home. Full clinical assessment and special investigations required for the diagnosis of different types of chorea, dystonia and athetosis were carried out in Assiut University Hospital. The prevalence rate for rheumatic chorea was 62/100,000 population and it was significantly higher (p < 0.01) among rural than urban and suburban populations, whereas Huntington''s chorea had a prevalence rate of 21/100,000 with no significant difference between different areas studied (urban, suburban and rural). The other two common types of chorea were reported with prevalence rates of 12/100,000 for the encephalitic type and 17/100,000 for the atherosclerotic type. No single case of generalized dystonia was recorded and all cases were of the focal type of dystonia with a prevalence rate of 26/100,000 population. No significant differences were recorded between the different areas studied (urban, suburban and rural). Idiopathic form and drug-induced form were the most prevalent types of focal dystonia (10/100,000). The prevalence rate of athetotic cases (all of which are postencephalitic) in our study was 12/100,000 with no significant difference between different areas studied (urban, suburban and rural).