Previous research has identified possible sex-based differences in restricted and repetitive behaviors in autism spectrum disorder (ASD). However, this finding is mixed, particularly among preschool-aged children. We investigated the presence of sex-based differences in parent-rated ASD symptomatology, using the Autism Spectrum Rating Scale (ASRS). Participants consisted of a large (n = 481,100 female), clinically-referred sample of preschoolers (ages 2-5) diagnosed with ASD (NVIQ: M = 67.11, SD = 21.79). Females had less severe symptoms on the Total, Unusual Behaviors, DSM-5, and Stereotypy scales on the ASRS. The effects were small-to-medium, but statistically significant. There was evidence of differential relationships between nonverbal IQ and ASRS scores among males and females. This study provides additional evidence of sex-based differences in ASD symptoms present from an early age.