Objective: Mortality is increased in bipolar disorder due to both suicide and death by physical disorders, but it has never been investigated whether these mortalities translate into relatives to patients with bipolar disorder. The aim was to present the life expectancy and the overall mortality and mortality due to suicide and physical disorders among patients with bipolar disorder and their unaffected full siblings, respectively, compared with control individuals from the general population. Methods: We used Danish nation-wide population-based longitudinal register linkage to identify 19.955 patients with bipolar disorder, their 13.923 siblings and 20 sex, age and calendar matched control individuals from the general population. Follow-up was from 1995 to 2017. Results: Bipolar disorder was associated with a decreased life expectancy of 7.7 (95% CI: 7.4-8.1) years and increased mortality overall (hazard ratio (HR): 2.11 (95% CI: 2.04-2.18)) and due to suicide (HR: 18.23 (95% CI: 15.81-21.02) and physical disorders (HR: 2.01 (95% CI: 1.94-2.08). In contrast, siblings to patients with bipolar disorder who were unaffected by bipolar disorder did not have decreased life expectancy (0.45 (95% CI: -6.622.46)) or increased mortality overall (HR: 1.00 (95% CI: 0.88-1.14) or due to suicide (HR: 1.50 (95% CI: 0.952.36) or physical disorders (HR: 0.99 (95% CI: 0.87-1.34). Conclusions: Increased mortality in bipolar disorder is mainly due to the impact of bipolar psychopathology and to a lesser degree to familial transmitted factors, highlighting the urgent need for preventive intervention studies in relation to suicide and physical disorders following onset of bipolar disorder.