To explore successful aging and high social activity in old age, data from a self-administered survey of 5,239 participants aged 65 years or more were analyzed. The questionnaire inquired about physical conditions and lifestyles of Japanese seniors during middle age and their present social activities in 4 regions of Japan in 1993. The authors first defined social activities and then developed a social-activity measure. Next, they examined the association between present social activity and physical conditions and lifestyles during middle age. Data analysis revealed that the most socially active seniors rated themselves as healthy and physically active during middle age. Socially active seniors differed from less active seniors: They had participated in more hobbies during middle age, had higher levels of education, and had had a more varied diet between the ages of 30 and 50. The data suggest that maintaining general health habits and lifestyles from middle age on is important for successful aging and high social activity in old age.