Background. The relationship between ethnicity and suicide risk is ill-understood. It is unclear whether, and if so, how, the ethnic mix of local areas affects risk in local individuals.

Methods. Coroners' records of 329 suicides were used to obtain ethnic (White, Afro-Caribbean, Asian) suicide rates in South London (population 902008) for 1991–3. Geographical variation and associations of ethnic suicide rates with small area (mean population 8274) ethnic densities (proportion of residents of given ethnic groups) and deprivation, were examined with random effects Poisson regression.

Results. Adjusted for deprivation, age and gender, suicide rates in wards with larger minority groups were higher among Whites (relative rate (RR) per standard deviation (S.D.) increase in minority density 1·18; 95% CI 1·02–1·37) but lower among minority groups (RR 0·75 (0·59–0·96)) (LR-test for interaction χ2=9·2 (df=1); P=0·003). Similar patterns were also apparent for Afro-Caribbeans and Asians separately. With White suicide rates as baseline, ethnic minority status is a risk factor for suicide in wards with small, but a protective factor in neighbourhoods with large minority populations. The RR of minority versus White suicide declines with a factor (relative RR) 0·67 (0·51–0·87) per S.D. increase in local minority density.

Conclusions. Minority suicide rates are higher in areas where minority groups are smaller. This effect is ethnic-specific and not due to confounding by gender, age, deprivation or unbalanced migration. Dependent on address, a suicide risk factor for a White individual may protect an ethnic minority individual and vice versa. This has implications for research and prevention.