Previous findings have suggested that the loss of a family member is associated with mortality among bereaved family members. The least-studied familial relationship in the bereavement literature is that of siblings, although loss of a sibling may also involve health consequences. The authors conducted a follow-up study based on data from the Swedish total population register, covering the period 1981-2002. Using Cox regression, mortality risk ratios for bereaved and nonbereaved persons aged 18-69 years were estimated. All-cause mortality and cause-specific mortality (unnatural causes, natural causes, cardiovascular disease, cancer, suicide, accidents, and all other causes) were examined. In men, the mortality risk for bereaved persons versus nonbereaved persons was 1.26 (95% confidence interval: 1.22, 1.30), and in women it was 1.33 (95% confidence interval: 1.28, 1.39). An elevated mortality risk associated with a sibling's death was found in all age groups studied, but the association was generally stronger at younger ages and could be observed predominantly after more than 1 year of follow-up. There was also an increased mortality risk if the sibling had died from a discordant main cause, which may strengthen the possibility that the association observed is not due to confounding alone.