Background: Retirement is a key life event, which is associated with changes in physical activity, however, there is limited evidence with regard to changes in physical activity that take place in post-retirement years. The aim of this study was to examine how leisure-time physical activity changes shortly after the transition to retirement and during the post-retirement years. Methods: The phase 1 data were collected in 2000-2002 (n = 8960, response rate 67%) among 40-60-year-old employees of the City of Helsinki, Finland. Phase 2 was carried out in 2007 (n = 7332, response rate 83%) and phase 3 in 2012 (n = 6814, response rate 79%). Disability retirees and those under the age of 50 at baseline were excluded. This yielded 2902 participants...