The excess mortality of schizophrenia is well recognised, but its precise causes are not well understood. To measure the standardised mortality ratio (SMR) and examine the reasons for any excess mortality in a community cohort with schizophrenia. We carried out a 13-year follow-up of 370 patients with schizophrenia, identifying those who died and their circumstances. Ninety-six per cent of the cohort was traced. There were 79 deaths. The SMRs for all causes (298), for natural (232) and for unnatural causes (1273), were significantly higher than those to be expected in the general population, as were the SMRs for disease of the circulatory, digestive, endocrine, nervous and respiratory systems, suicide and undetermined death. Smoking-related fatal disease was more prominent than in the general population. Some of the excess mortality of schizophrenia could be lessened by reducing patients' smoking and exposure to other environmental risk factors and by improving the management of medical disease, mood disturbance and psychosis.