Published healthcare cost estimates for children with autism spectrum disorder (ASD) vary widely. One possible contributor is different methods of case ascertainment. In this study, ASD case status was determined using two sources of parent reports among 45,944 children ages 3-17 years in the Medical Expenditure Panel Survey (MEPS) linked to the National Health Interview Survey (NHIS) Sample Child Core questionnaire. In a two-part regression model, the incremental annual per-child cost of ASD relative to no ASD diagnosis was $3930 (2018 US dollars) using ASD case status from the NHIS Child Core and $5621 using current-year ASD case status from MEPS. Both estimates are lower than some published estimates but still represent substantial costs to the US healthcare system.