There is almost no previous empirical research addressing the role of fathers in children's risk for unintentional injury, the leading cause of pediatric mortality in the United States. This study examined the role of fathers transitioning into or out of the household in young children's subsequent injury risk. One thousand sixty children were divided into four groups based on the presence, absence, or transition of fathers (or father-figures) between the time children were 6 and 36 months: those whose fathers were present throughout, those whose fathers were absent throughout, those who experienced a father joining the household, and those who experienced a father leaving the household. Injuries were recorded regularly from 36 months until the end of first grade. Results suggest children who experienced the entry of a father into the home during toddlerhood experienced significantly lower rates of subsequent injury than children whose parents remained absent or present, or who experienced the departure of a father. This finding held true even after including a range of established child-, parent-, and family-oriented risks for child injury in a multivariate model. Theoretical and applied implications are discussed. © 2007 American Psychological Association.