One of the most important lines of research on unselected large scale twin registries are mortality follow-ups. Death-specific concordance rates have been calculated using different measures of concordance. These estimates are of great importance but they only reflect an “all or-none” classification of the genetic effect. It is suggested that mortality studies could be extended to, and include studies on, death-discordant twins. Such studies combine the advantages from mortality follow-ups on total twin populations with the detailed clinical investigation on subsamples. By examining the surviving cotwins with respect to various traits and supposed risk factors, an opportunity has been provided to study the genetic determination on the development of disease. This approach has been used in a study of ischaemic heart disease (IHD) and its risk factors in a representative subsample from the Swedish Twin Registry.