Background: There is currently little consensus on how the severity of a child’s autism spectrum disorder (ASD) should be measured, and yet despite the lack of a standardized definition, parents were readily able to answer a question asking them to describe the severity of his/her child’s ASD in a national survey. Objective: The current study examined factors associated with a parent’s judgment of ASD severity, by identifying child and household characteristics that were associated with a parent’s severity rating of his/her child’s ASD, including child ASD symptomatology, child impact, and family impact. Methods: Data came from the 2011 Survey of Pathways to Diagnosis and Services (‘Pathways’). A total of 967 parents in households with a child diagnosed with ASD between the ages of 6-17 were eligible for the current study. A measurement model was used to create latent factors of child symptoms, child impact, and family impact; multivariate logistic regression models examined the relationship between these latent factors and the parent’s severity rating of their child’s ASD. Results: Children with higher family impact factor scores were more likely to have parents who rated their child’s ASD as the most severe. Surprisingly, symptomatology and impact on the child were less predictive of severe ratings. Conclusions: A parent’s conceptualization of their child’s ASD severity may vary more as a function of the impact of the child’s condition on the family and less as a function of the symptoms exhibited by the child or the impact directly felt by the child.