This is a randomized, double blind, placebo-controlled study of the effects of intranasal oxytocin on bone health in children with autism spectrum disorder, ages 6-18 years old. Subjects will be randomized to receive intranasal oxytocin or placebo (30 IU, 2 times daily) for 12 months in the double-blind phase, followed by a 6-month open label phase during which all study subjects will receive intranasal oxytocin (30 IU, 2 times daily). Study visits include screening to determine eligibility, followed by study visits at baseline, week 2, and months 6, 12, 18 and phone calls every two weeks for the first two months and monthly thereafter for the duration of the study. Study assessments include history and physical examinations, anthropometric measurements, electrocardiogram (EKG), adverse event monitoring, laboratory tests for chemistries, hormones and biomarkers for bone metabolism, questionnaires regarding diet and exercise, and imaging to assess body composition, bone density and structure.