This study investigated the stability of Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) classifications in a cohort of 304 siblings at elevated likelihood for autism (EL-siblings).ADOS-2 assessments were conducted at 14, 24 and 36 months, with Clinical Best Estimate (CBE) autism diagnoses determined at 36 months.Our findings indicate that while some children have stable ADOS-2 classifications from early on, a significant proportion of the children show inconsistent classifications over time. The overall stability of ADOS-2 autism spectrum classifications increased from 14 to 36 months and agreement with CBE autism clinical diagnosis was moderate and increased with age.Caution is warranted when interpreting individual ADOS-2 results, as they should always complement, and can never replace, a comprehensive clinical evaluation. These findings highlight the importance of continued follow-up beyond 14 months in young EL-children, a group for whom early assessment may be both feasible and beneficial and emphasises the need to integrate multiple assessment measures and multiple informants for accurate early autism identification.
