Clinical anxiety disorders in youth are common and associated with interpersonal behaviors including reliance on parents for family accommodation, or changes that parents make to their own behaviors to help the youth avoid anxiety related distress. The neuropeptide oxytocin is associated with the regulation of anxiety and of close interpersonal behavior leading to the hypothesis that oxytocinergic functioning plays a role in youth anxiety and its disorders, and the resulting family accommodation. To test this hypothesis salivary OT from 50 youth with primary DSM-5 anxiety disorders was assayed. A multi-source/multi-method anxiety assessment including semistructured interviews with youth and mothers, rating scales, and behavioral observations was used to assess anxiety disorders and symptoms, and family accommodation. Youth with separation anxiety disorder had significantly lower salivary OT levels than clinically anxious youth not diagnosed with separation anxiety disorder. Salivary OT levels were significantly negatively correlated with separation anxiety symptoms based on both youth- and mother-ratings. Anxious behavior displayed by youth during interactions with their mothers was associated with lower salivary OT levels in youth. Maternal ratings of family accommodation were negatively associated with salivary OT levels in youth. Results support the role of the oxytocinergic system in youth anxiety and its disorders and in parental involvement in youth anxiety through family accommodation. OT may be particularly important for diagnoses and symptoms of separation anxiety, which is inherently interpersonal in nature. Findings have potentially important implications for assessment and treatment of anxiety in youth.