BACKGROUND:

Urbanicity is a risk factor for schizophrenia, but it is unclear whether this risk is homogenous across urban areas.

AIMS:

To determine whether the incidence of psychotic disorders varied within an urban area, beyond variation attributable to individual-level characteristics.

METHODS:

All incident cases of ICD-10 psychoses from a large, 2-year, epidemiological study of first-episode psychoses in Southeast London were identified. Incidence rates for 33 wards were standardised for age, sex and ethnicity. Bayesian models produced accurate relative risk estimates that were then mapped.

RESULTS:

295 cases were identified during 565,000 person-years of follow-up. We observed significant heterogeneity in relative risks for broad and non-affective psychoses (schizophrenia), but not for affective psychoses. Highest risks were observed in contiguous wards.

CONCLUSIONS:

Neighbourhood variation in the incidence of non-affective psychoses could not be explained by individual-level risk, implicating neighbourhood-level socioenvironmental factors in their aetiology. The findings are consistent with classical sociological models of mental disorders.