Previous studies have examined the relationship between sleep problems and challenging behaviors in school-aged children and adolescents with autism spectrum disorder (ASD). However, literature has not examined this relationship in the context of toddlers or, more specifically, toddlers with aggression. The present study was conducted to examine the relationship between ASD severity, sleep problems, and aggression in toddlers (aged 24 to 36 months) with a diagnosis of ASD. Sleep problems were measured by the Childhood Sleep Habits Questionnaire (CSHQ; NICHD SECCYD-Wisconsin, 2017) and aggression was measured by part 3 of the Baby and Infant Screen for Children with aUtism Traits (BISCUIT; Matson et al., 2007). A hierarchical multiple regression was conducted with a sample of 28 toddlers and the results indicated sleep problems statistically significantly predicted aggression over and above ASD severity. Implications of these findings and future research directions are discussed.