Background. The heterogeneity of schizophrenic and delusional syndromes by age of onset has frequently been discussed.

Methods. The age distribution of symptoms and 5 year course was studied in a population-based first-episode sample admitted to 10 psychiatric hospitals before the age of 60 (N=232) and in a clinical sample without age limit of consecutive first admissions to a single hospital (N=1109), both samples with broadly diagnosed schizophrenia.

Results. Early-onset patients, particularly men, presented more non-specific symptoms and higher PSE-CATEGO total scores than late-onset patients. In men, symptom severity decreased with increasing age of onset. In women, it remained stable except for an increase of negative symptoms with late-onset. Only a few symptoms changed markedly with age: disorganization decreased, while paranoid and systematic delusions increased steeply across the whole age of onset range. Pronounced age- and sex-differences emerged in illness behaviour, socially negative behaviour and substance abuse. Within the group of late-onset psychoses there were continuous transitions in symptom profiles and no discrimination between schizophrenia and paranoid psychosis or late paraphrenia. The main determinant of social course was onset level of social development. Early-onset patients did not improve in social status, while late-onset patients, prior to retirement, suffered considerable decline in social status.

Conclusions. Gender differences in age at onset and in age trends in symptom severity support the hypothesis of a mild protective effect of oestrogen. Social course results from an interplay between biological factors (age at onset and functional impairment) and development factors (level of social development at onset and illness behaviour).