We examined the mortality of the birth cohorts born 1880–1957 in the like-sexed twin pairs of the older twin cohort, in which both twins were alive and resident in Finland in 1975. The beginning of follow up was 1 May 1976, and end of follow-up is death, emigration or alive at end of follow up in 31 December 2009. National mortality rate by five-year age groups and five year calendar periods were obtained from the Human Mortality Database (www.mortality.org). Standardized mortality ratios (SMR) were computed as the ratio of observed to expected (based on person years and population rates). The overall SMR for male twins was 94.95 (95% CI 92.3 to 97.7, based on 4752 deaths) compared to 100 for the population, while for female twins it was 94.5 (91.5 to 97.6, 3714 deaths). MZ twins had the lowest SMRs (87.2 for men, 89.5 for women), DZ twins somewhat higher (94.0 for men and 94.3 for women), while the small number of twins with unknown zygosity had higher than expected mortality (SMR for men was 113 based on 810 deaths
