More than one in ten American grandparents raise a grandchild for at least six months, with most of these providing care for three years or more. This longitudinal study, utilizing data from the National Survey of Families and Households, identifies the pre-existing personal characteristics and contextual variables which are predictive of individuals becoming primary caregivers for their grandchildren. Contrary to hypothesis, pre-caregiving attitudes concerning intergenerational solidarity bore little relationship to the likelihood of becoming a caregiver. In contrast, being female, younger, African American, and having not completed high school were significantly predictive of becoming a custodial grandparent. Implications of these findings for research, practice, and policy in gerontology, mental health, and related areas are discussed.