The schizophrenia programme included three major studies. The first was the International Pilot Study of Schizophrenia, which involved nine centres in Africa, Asia, Europe, and North America, with a total of 1,202 patients aged 15–44. The second World Health Organization (WHO) study aimed to explore the behavioural impairments and social disabilities in schizophrenic patients of onset. The third study, bearing the title ‘Determinants of Outcome of Severe Mental Disorders’, had a more complex design and included 1,379 patients assessed at twelve research centres in ten countries. The spectrum of psychopathology of schizophrenia also includes variations in the presentation of the disorder in the different cultures. Schizophrenia appears to behave differently from other multifactorial diseases like diabetes or ischaemic heart disease, which show much greater variation in incidence both across and within populations. The WHO programme on comparative cross-cultural research in schizophrenia has succeeded in meeting most of these methodological requirements.