The population-based Gerontological Regional Database (GERDA) cohort study was initiated to investigate the health/disease status of very old people and factors leading to good aging in this population. Half of all 85-year-olds, all 90-year-olds, and all participants aged at least 95 years in selected municipalities of Västerbotten County, northern Sweden, were invited to participate. The first round of data collection was performed in an urban municipality in 2000 and in five adjacent rural municipalities in 2002. A second round of data collection was performed in 2005 and 2007 with the same inclusion criteria, meaning that all surviving past participants were eligible for reparticipation in older age groups. A third data collection was performed in 2010 and 2012.