Overlapping social impairments in Autism Spectrum Disorder (ASD) and Schizophrenia (SCZ) contributed to decades of diagnostic confusion that continues to this day in some clinical settings. The current study provides the first direct and detailed comparison of social behavior in the two disorders by identifying profiles of social skill in adults with ASD (n = 54), SCZ (n = 54), and typically developing (TD) controls (n = 56) during a real‐world social interaction. ASD and SCZ groups exhibited poorer social skill, both overall and on most discrete abilities, relative to the TD group. Direct comparison of ASD to SCZ revealed distinct behavioral profiles, with ASD uniquely characterized by fewer interactive behaviors, and SCZ characterized by greater impaired gaze and flat/inappropriate affective responses. Additionally, IQ was associated with both overall social skill and many discrete social skills in SCZ, but was largely unrelated to social skill in ASD. These results indicate that overlapping social deficits in ASD and SCZ are comprised of both shared and distinct social skill impairments. The largest distinctions—reduced social reciprocity but better expressivity in ASD relative to SCZ, and a greater role of IQ in social skill for SCZ than ASD—highlight disorder‐specific features that can improve etiological understanding, diagnostic differentiation, and treatment strategies. Autism Res 2017, 10: 878–887. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.