A total of 232 (84%) first episodes of schizophrenia from our epidemiologically defined ABC sample (Age, Beginning and Course) were retrospectively assessed with regard to the onset and early course of the disorder. In a follow-up study a representative subgroup (n = 133) was prospectively examined in five cross sections over 3 years from first admission on. Population-based incidence rates for 5-year age groups comprising a range of < 10 - < 60 years were calculated on the basis of two definitions of onset: first sign of disorder and first psychotic symptom. In 40% of adult patients who had been admitted with a first schizophrenic episode after age 20 years the prodromal phase, in 11% the psychotic prephase, began before that age. This demonstrates that schizophrenia often begins in an age period in which the social and cognitive development and brain maturation are still unfinished. Early-onset schizophrenias (< or = 20 years) were compared with a medium-onset group (21 - < 35 years) and a late-onset group (35 - < 60 years) with regard to age and type of onset, early symptom-related course, social development and social course. The number of schizophrenia-specific positive and negative syndromes in early-onset schizophrenia is comparable to that of higher age groups. However, neurotic syndromes, emotional disorders and conduct disorders are most frequent in younger patients, especially in young men. Paranoid syndromes seem to prevail in late-onset schizophrenia, whereas less differentiated positive syndromes, such as delusional mood, are more frequent in the youngest age group. An earlier onset of schizophrenia has more severe social consequences than onset in adults, because it interrupts the cognitive and social development at an earlier stage. The worse social course of schizophrenia in men compared with women cannot be related to a more severe symptomatology, but to the earlier age at onset and the impairment or stagnation of social ascent at an earlier stage of social and cognitive development. Social disability in the sense of an adaptation to the expectations of the social environment, as well as symptomatology during the further course of schizophrenia, show no major differences between the genders nor between the age groups.