A new standardised interview for the retrospective assessment of onset and early course of schizophrenia (IRAOS) was used to study the influence of age and sex on time of onset and psychopathology before first admission in 267 schizophrenic patients admitted for the first time. Mean age at onset, according to various operationalised definitions, differed by three to four years between the sexes. The age distribution at the earliest sign of mental disorder showed an early and steep increase until the age of 25 in males, and a delayed and smaller increase in females, with a second peak in women aged 45–79. Schizophrenia began with negative symptoms in 70% of cases, appearing two to six years before admission, and all positive symptoms appearing up to two years before. Both positive and negative symptoms accumulated exponentially. The early course of the disease was similar across age groups, except there was a longer period of negative symptoms before first admission in late-onset schizophrenia in women. The few significant age differences in symptoms were presumably due to general age-dependent reaction patterns like anxiety and depression or the cognitive development of personality, as indicated by an increase in fully elaborated positive symptoms, especially systematised paranoid delusions, with age.