Emotion regulation (ER) abilities and developmental differences were investigated among 19 children with autism and 18 children with 22q13 Deletion Syndrome (a rare chromosomal disorder with certain autistic symptoms). The purpose of this study was to examine the phenotypic similarities between the two disorders. ER was measured by the Temperament and Atypical Behavior Scale (TABS) and development was measured by the Developmental Profile--Third Edition (DP-3). It was hypothesized that children with autism would score higher on the Detached domain of the TABS because the domain is associated with autism spectrum disorders. It was also hypothesized that because of similarly well established cognitive and communicative deficits between the two populations, no significant differences in development would be found. Results indicated that the autism group was significantly more impaired on the Detached domain of the TABS and scored higher on every domain of the DP-3 except in social-emotional skills. These findings differentiate the phenotypes of the two disorders and suggest that detached emotional behavior is more salient among children with autism. Early intervention programs that target the improvement of ER and social skills may ensure healthier behavioral outcomes for these individuals. (Contains 5 tables.)