Emotion regulation (ER) in Autism Spectrum Disorder (ASD) is frequently identified as source of concern for ASD children within clinical treatment settings, but is rarely the primary research focus of clinical studies. Process-based theories of ER are common in literature based on typical development but have yet to be scientifically examined within atypical populations. The current study introduces the Emotion Regulation Assessment for Autism (ERAA) as an ASD-specific clinical measure of ER skills. The ERAA is based on existing, process-based theories of ER. ER difficulties in ASD are problematic for clinicians and families. The existence of an ASD-specific measure of emotion regulation may assist in intervention planning to prevent regulatory difficulties later in life. Participants include 31 children with ASD and 31 children with a history of typical development, all between 24 and 36 months of age. Children are observed in 15-minute, structured play samples with both a parent and a stranger. Play observations are recorded and reviewed by blind observers who provide behavioral codes via the ERAA and other behavioral coding schemas. ERAA codes are assessed across varying styles of play and partners (i.e., independent vs. joint-interactive style of play; stranger vs. parent). Additional information is collected via parent report and developmental assessments by a clinician. Primary analyses show reliable use of the ERAA by blind coders and significantly higher scores of ER difficulties within the ASD sample than in the sample with typical development. Within both samples, play context produces a notable difference in ER skills, as independent play shows participants having more difficulty with ER than either joint-interactive play or disruptive play. Secondary analyses support the utility of the ERAA as being a unique measure of ER for children with ASD. The assessed symptoms of ER difficulty on the ERAA appear to be separate from the traditional ASD symptoms but also distinct from traditional symptoms of ER. The results of the current study have important implications for assessing and treating ER difficulties in ASD, but are also indicative of future areas of ASD research, such as dysregulation during independent play.