Cardiac vagal tone (VT) was studied as a resilience factor in children prenatally exposed to cocaine and nonexposed controls (n = 550). A cumulative risk index was derived and used to classify children as high versus low risk. VT was measured during mildly stressful observations at 1 and 36 months of age. Children were classified as having consistently high, consistently low, or fluctuating VT. Risk and VT interacted to predict adaptive behaviors. For high-risk children, low VT was related to higher ratings of adaptive behaviors. This finding suggests that regulatory functioning, as indexed by VT, may be a protective factor in prenatal CE.