The commonly used Vineland Adaptive Behavior Scales (VABS-3) divides adaptive behavior into three domains comprising three subdomains. The validity of this three-factor structure has not been explored in autistic samples, which are often heterogeneous with respect to language and IQ. Furthermore, although there are two comparable forms, Comprehensive Interview Form and Comprehensive Parent/Caregiver Form (a questionnaire), the original validation was based on interview data. Considering the widespread use of the VABS-3 in autism research, and the increased feasibility of online-administered questionnaires, it is necessary to establish the validity of the Parent/Caregiver form in autistic individuals across a range of abilities. This study aimed to investigate the measurement invariance of the VABS-3 Parent/Caregiver form between a minimally verbal group and verbal group of autistic people; however, poor overall fit of the three-factor structure precluded invariance analyses. Subsequent analyses suggested poor fit in both language and age groups, as well as a unidimensional model. The results of the current study suggest that neither the three-factor or unidimensional model fit the VABS-3 Parent/Caregiver Form, thereby cautioning against interpretation of domain or overall adaptive behavior composite scores in autistic individuals and further encouraging careful consideration of administration format.