An independent validation was conducted of the Utah Autism and Developmental Disabilities Monitoring Network's (UT-ADDM) classification of children with autism spectrum disorder (ASD). UT-ADDM final case status (n = 90) was compared with final case status as determined by independent external expert reviewers (EERs). Inter-rater reliability (ICC = 0.84), specificity [0.83 (95 % CI 0.74-0.90)], and sensitivity [0.99 (95 % CI 0.96-1.00)] were high for ASD case versus non-case classification between UT-ADDM and EER. At least one EER disagreed with UT-ADDM on ASD final case status on nine out of 30 records; however, all three EERs disagreed with UT-ADDM for only one record. Findings based on limited data suggest that children with ASD as identified by UT-ADDM are consistently classified as ASD cases by independent autism experts.