As part of a World Health Organization collaborative study in 12 centres in developing and developed countries within defined urban and rural catchment areas with populations of 348,786 and 103,865, respectively, a total of 155 and 54 cases of first-onset schizophrenia, respectively, were identified over a 24-month period by a comprehensive and active recruitment of all cases. Approximately 50% of the subjects in both cohorts were in the age range of 15-24 years. There was a preponderance of males in the younger age group and of females in the older age group. The majority of cases had no family history and had shown good adjustment in childhood and adolescence. The onset was much more frequently acute and much less often insidious in our samples and (more so in the rural cohort), compared to the figure for all developed countries' sites. With regard to early manifestations of the disorder, there was a much higher incidence of loss of interest in appearance and cleanliness, being irritable and angry without reason, and loss of appetite, sleep or interest in sex in both of our samples, and of being excited or overactive for days or weeks in our rural cohort than in the developed countries' centres as a whole. On the other hand, claiming impossible things, behaving as if hearing voices and feeling persecuted, harmed or bewitched were much less frequent in our rural cohort than in the urban cohort or the developed countries' centres as a whole. With regard to the clinical diagnosis of schizophrenia, paranoid, hebephrenic/disorganized and residual types were under-represented in our samples (more so in the rural sample), and catatonic type and acute schizophrenic episode were over-represented compared to the developed countries' centres. Moreover, the proportion of subjects of CATEGO class S+ was lower in our samples. With regard to onset, early manifestations and clinical subtypes of schizophrenia, our rural cohort deviated most from developed countries' centres as a whole, with our urban sample falling in between, thus indicating the role of socio-cultural factors in general, and urbanization in particular, in these variables in schizophrenia.
