BACKGROUND: The association between social inequality at birth and subsequent risk of schizophrenia is uncertain. AIMS: To investigate the relationship between adult-onset schizophrenia and two indicators of social inequality at birth: social class and area of residence. METHOD: A matched case-control design was used with data from birth certificates of first-episode cases and age- and gender-matched controls. RESULTS: Risk increased with increasing levels of deprivation at birth. Subjects whose fathers were social class IV-V or who were born in deprived areas were at increased risk of schizophrenia (odds ratio=2.1; 95% Cl=0.8-5.5). Risk was greater in those with both of these indicators (odds ratio=8.1; 95% Cl=2.7-23.9). There was some evidence that associations were stronger in older subjects. Exclusion of African-Caribbeans or cases with positive family history somewhat attenuated the association. CONCLUSIONS: Indicators of social inequality at birth are associated with increased risk of adult-onset schizophrenia, suggesting that environmental factors are important determinants of schizophrenic disorders.