The effect of bereavement on mortality among surviving spouses was examined in a cohort of 12,522 spouse pairs belonging to a prepaid health care plan in northern California. Both spouses were examined and completed a questionnaire between 1964 and 1973, and they were followed for mortality through 1987. Between 1964 and 1987, 1,453 men (12%) and 3,294 women (26%) were bereaved; 440 bereaved men (30%) and 510 women (15%) died during follow-up. Mortality following bereavement was significantly elevated in both men and women after adjusting for age, education, and other predictors of mortality in proportional hazards analyses. The highest relative risks (RRs) of mortality occurred 7-12 months following bereavement. Among women, the RR was 1.9 (95% confidence interval (CI) 1.35-2.71) 7-12 months after bereavement. Among men, the effect of bereavement interacted with prior health status as follows: In men with few health problems, the RR of mortality was 2.12 (95% CI 1.42-3.17); men with many health problems had a RR of 1.56 (95% CI 0.98-2.55) 7-12 months after bereavement. In both men and women, the RR declined after the first year of bereavement but remained above 1.0 for more than 2 years after bereavement. The addition of terms reflecting the influence of the other spouse's characteristics and behaviors did not alter the RR of mortality, indicating no effect of a shared unfavorable environment on mortality following bereavement.