TG and autism: <h4>Context</h4>Thyroid hormones affect neurological development and function, but detailed studies of thyroid hormones and metabolites in autism are lacking.<h4>Objective</h4>To characterize thyroid function and metabolism in autistic children.<h4>Methodology</h4>This cross-sectional study compared 788 autistic children (mean age 7.6 ± 3.9 years, 78% male) with 301 non-autistic children (mean age 7.8 ± 4.0 years, 48% male; comprising 215 (71.4%) non-autistic siblings of participants and 86 (28.6%) unrelated individuals).