["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nThis 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).\n\n\nMethods\nADOS‐2 assessments were conducted at 14, 24 and 36 months, with Clinical Best Estimate (CBE) autism diagnoses determined at 36 months.\n\n\nResults\nOur 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.\n\n\nConclusions\nCaution 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.\n\n"]