This study investigated differences in co-occurring diagnoses made in females compared to males with autism spectrum disorders in 913 children (746 males and 167 females) living in the United States with a current autism spectrum disorder diagnosis identified via caregiver-reported data from the National Survey of Children’s Health 2007. The results indicated that overall, females had significantly fewer reported autism spectrum disorder co-occurring conditions than males. Females, compared to males, with a current autism spectrum disorder diagnosis had lower rates of past learning disorder, current mild learning disorder, and past anxiety diagnoses. Females with a current autism spectrum disorder diagnosis were more likely than males to have been diagnosed with a speech problem in the past, while males with a current autism spectrum disorder diagnosis were more likely than females to have a current diagnosis of a mild learning disability and a past diagnosis of learning disability. In addition, males with a current autism spectrum disorder diagnosis were more likely than females to have two or more co-occurring diagnoses. These findings provide insight into trends in sex differences in autism spectrum disorder co-occurring conditions.