This study investigated whether family structure transition and low income are risk factors in the development of prosocial behavior. Models of young adults' prosocial behavior--charitable giving and volunteering--were estimated as functions of their family structure and income during the stages of childhood. Participants were a representative sample of 1011 American young adults. In the full sample, family structure transition during adolescence was negatively associated with subsequent charitable giving in young adulthood. Low income during adolescence was negatively associated with both giving and volunteering in young adulthood. European-American young men also exhibited a negative association between family structure transition during adolescence and subsequent volunteering. The results did not seem to describe African-American young adults. Keeping this qualification in mind, the results suggest that adolescence is a sensitive stage in the development of charitable giving and volunteering. (Contains 5 tables.)