Understanding adaptive functioning profiles in children with Williams syndrome (WS) and autism spectrum disorder (ASD) is critical to inform treatment strategies. However, knowledge in this area is limited and inconclusive. The current study aimed to characterise the early adaptive profiles of young children with WS (n = 18; Mage = 47 months) and ASD (n = 26; Mage = 45 months) matched on chronological age and developmental age using the Vineland Scales of Adaptive Behavior, Second Edition. Results suggest that young children with WS and ASD do not differ on their overall level of adaptive functioning but that those with WS show relative strengths in the Socialisation scale compared with children with ASD. No other subscales differed between groups. Within groups, the WS group showed a profile of Communication, Daily Living Skills and Motor < Socialisation, whereas the ASD group did not evidence differences across subscales. Consideration of the shared and syndrome-specific adaptive profiles provides relevant insight on intervention targets and strategies. Given the shared challenges across the two clinical groups, implications and future directions are discussed. © 2019 MENCAP and International Association of the Scientific Study of Intellectual and Developmental Disabilities and John Wiley & Sons Ltd.