Despite the early onset of challenging behaviors, there is a lack of research investigating the function of challenging behavior in toddlers with autism spectrum disorder (ASD) and developmental disabilities (DDs). The current study evaluated group differences in the frequency and severity of five functions of challenging behavior (i.e., Attention, Escape, Nonsocial, Physical, Tangible). A total sample of 98 toddlers, aged 19-40 months, were classified into the ASD group or the atypical development group. No group differences were found in regard to the reported frequency of the function of behavior. Group differences in the severity of the function of behavior were found in the Attention function only. Significant differences across ASD symptom severity groups were also found in the Attention and Nonsocial functions. Clinical implications of the current findings are discussed.