Rationale: Biopsychosocial models of asthma have been proposed in the literature, but few empirical tests of social factors at various levels of influence have been conducted. Objective: To test associations of neighborhood, peer, and family factors with asthma outcomes in youth, and to determine the pathways through which these social factors operate.Methods: Observational study of youth with asthma (n=78). Measurements: Youth completed questionnaires about neighborhood problems, peer support, and family support. Biological (IgE, eosinophil count, production of IL-4) and behavioral (youth smoking, exposure to smoke, adherence to medications) pathways were measured. Asthma symptoms and pulmonary function were assessed in the laboratory and at home for 2 weeks. Main Results: Lower levels of family support were associated with greater symptoms and poorer pulmonary function via biological pathways. Higher levels of neighborhood problems were associated with greater symptoms via behavioral pathways related to smoking. Peer support was not associated with symptoms or pulmonary function. Conclusions: These findings suggest that family factors may affect youths' asthma via physiological changes, whereas community factors may help shape the health behaviors of youth with asthma.