Autism spectrum disorder (ASD) research is largely based on males, and females with ASD are at risk for under-identification. Research recommends listening to parent concerns since these are often predictive of a child's eventual diagnosis. This study examined how patterns of parent concerns predicted sex differences and eventual child diagnosis (ASD or developmental delay [DD]). We performed a secondary analysis with n = 273 children ages 36-72 months. Results suggested males with ASD had a higher likelihood of repetitive behavior and speech and language concerns compared to females with ASD. Females with DD were significantly more likely to have problem-solving concerns; whereas, males with DD were significantly less likely to have social communication concerns compared to females with ASD.