Purpose: No diagnostic tools exist for identifying social (pragmatic) communication disorder (SPCD), a new "Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition" category for individuals with social communication deficits but not the repetitive, restricted behaviors and interests (RRBIs) that would qualify them for a diagnosis of autism spectrum disorder (ASD). We explored the value of items from a widely used screening measure of ASD for distinguishing SPCD from typical controls (TC; Aim 1) and from ASD (Aim 2). Method: We applied item response theory (IRT) modeling to Social Communication Questionnaire--Lifetime (Rutter, Bailey, & Lord, 2003) records available in the National Database for Autism Research. We defined records from putative SPCD (n = 54), ASD (n = 278), and TC (n = 274) groups retrospectively, based on National Database for Autism Research classifications and Autism Diagnostic Interview--Revised responses. After assessing model assumptions, estimating model parameters, and measuring model fit, we identified items in the social communication and RRBI domains that were maximally informative in differentiating the groups. Results: IRT modeling identified a set of seven social communication items that distinguished SPCD from TC with sensitivity and specificity > 80%. A set of five RRBI items was less successful in distinguishing SPCD from ASD (sensitivity and specificity < 70%). Conclusion: The IRT modeling approach and the Social Communication Questionnaire--Lifetime item sets it identified may be useful in efforts to construct screening and diagnostic measures for SPCD.