Social anxiety disorder (SAD) is commonly comorbid with autism spectrum disorder (ASD). Here, in a sample of 86 children and adolescents (M[subscript 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.