This article uses data on 2,024 men who were followed through the third wave of the National Survey of Families and Households to examine the implications of fatherhood experiences for men's involvement in altruistic social activities at middle age. We find that middle-aged men (ages 45-65) who at some point in their lives become fathers are significantly more likely to have altruistically oriented social relationships and be involved in service organizations compared with men who have never become fathers. Furthermore, it appears that the defining aspect of the effect of fatherhood is the level of engagement with children while they are growing up. Neither current residential status nor whether current nonresidence occurs because of nest leaving is found to distinguish men's altruistic ties. (Contains 4 tables and 1 figure.)