Studies of parental influence on children's physical activity have had different results. Parental effect on physical activity during adolescence is less studied, and three generation studies have not been carried out. The purpose of our study was to examine intra- and intergenerational associations of leisure time physical activity among family members in three generations. Due to the major changes in society during this time, we also took into consideration the socioeconomic status of the adult subjects. The material consisted of 3254 twins at the age of 16, their parents and grandparents. Twins and their parents received a questionnaire in 1991-1993, which included questions about the health and lifestyle, socioeconomic status and leisure time physical activity. The parents' questionnaire also included questions about their own parents' leisure time physical activity and socioeconomic status. Based on these questions adolescents, parents and grandparents were classified into physical activity classes. The socioeconomic classification of parents and grandparents was based on their occupation. Intragenerational physical activity patterns were significantly associated with each other. Among adolescents the strongest correlation were between monozygotic boys (0.720) and monozygotic girls (0.638). Physical activity patterns were not associated between generations, but there was a significant difference between very active and inactive mothers concerning their daughters' physical activity. Farmers had the lowest proportion of very active subjects only among the parental generation. Because physical activity patterns do not appear to be transmitted from one generation to the next, it is probable that by constant training and education we can obtain the benefits of physical activity.