The Older Finnish Twin Cohort was established 50 years ago and includes twins born in Finland before 1958. Members of the cohort have responded to detailed questionnaires about their health, habits, and lifestyle up to four times, in 1975, 1981, 1991, and 2011. In 2019, the Finnish Parliament approved the Act on the Secondary Use of Health and Social Data, which enables wider use of data from national social and healthcare registers as well as various patient systems and social services. This data resource article describes the linkage of the Older Finnish Twin Cohort to numerous social and healthcare registers, alongside linked data from their families and the broader Finnish population born in 1945−1957, which serves as a reference population for generalizability and other analyses.