Social anxiety disorder (SAD) is commonly comorbid with autism spectrum disorder (ASD). Here, in a sample of 86 children and adolescents ( M AGE  = 12.62 years; 68.6% male), 28 of whom were diagnosed with ASD, 34 with SAD, and 24 with comorbid ASD and SAD, we compared parent-reported scores from the Social Responsiveness Scale-Second Edition (SRS-2; Constantino and Gruber in Social Responsiveness Scale (SRS; Constantino and Gruber 2012 ) to determine the sensitivity and specificity of the measure in cases of differential diagnosis between SAD and ASD. Results suggest that neither the subscales, nor the SRS-2 total score, consistently differed between ASD and SAD. Sensitivity and specificity analyses suggested that the SRS-2 total poorly discriminated ASD from SAD. When screening socially anxious youth for possible ASD, caution should be taken.