Despite a growing literature documenting deleterious intergenerational consequences of incarceration, relatively little is known about how exposure to paternal incarceration is associated with risk behaviors in adolescence. In this article, we use data from the Fragile Families and Child Wellbeing Study (N = 3405)—a cohort of urban children born around the turn of the twenty-first century and followed for 15 years—to examine the relationship between paternal incarceration and one indicator of adolescent risk behavior, early sexual onset. Results from adjusted logistic regression models show that paternal incarceration is associated with a greater likelihood of initiating sexual activity before age 15, in part resulting from externalizing problems that follow paternal incarceration. We also find that these associations are concentrated among boys living with their fathers prior to his incarceration. Given that paternal incarceration is a stressor concentrated among already vulnerable children, paternal incarceration may exacerbate inequalities in adolescent sexual risk behavior.