Researchers increasingly recognize the importance of neighborhoods as a potential cause of noncommunicable disease, although the long-term impacts of early neighborhood exposures are not well understood. We used data from the prospective, nationally representative National Longitudinal Study of Adolescent to Adult Health to calculate correlations in health outcomes during adulthood among individuals who attended the same school in adolescence. These upper-bound estimates suggest that the amount of variation attributable to early neighborhoods is small in the case of adult obesity and depressive symptoms and small or modest in the case of cardiovascular risk in early adulthood. Taken together, our results suggest that the benefits of neighborhood-based interventions during adolescence in alleviating the burden of these noncommunicable diseases are likely to be relatively small. Our methods also provide a useful framework for future work that seeks to produce similar estimates on other adult conditions and for future policy discussions that attempt to compare the likely impacts of early neighborhood-level interventions across various adult outcomes.