Background: A key element of the evidence-based assessment and treatment movements is ensuring an adequate representation of clients across the different settings in which they receive mental health care (e.g., research and routine or usual care settings). Prior work has focused on comparing clients from research settings to those from usual care settings on various indices of clinical severity, impairment, and symptom levels. Objective: In this study, we focused on examining clients from different types of research studies not only on levels of clinical severity, impairment, and symptoms, but also on the relations among these domains. Methods: We addressed our objective in a sample of 73 youths meeting primary diagnostic criteria for generalized anxiety disorder (GAD); n = 32 were recruited specifically for a treatment study or received services from a university-based clinic ("Youths Receiving Treatment"; "YRT"), and n = 41 were recruited for a non-treatment assessment study ("Non-Treatment Research Youths"; "NTRY"). Results: Relative to NTRY, YRT displayed greater GAD clinical severity, and higher generalized anxiety and worry levels. However, we observed no differences between groups in relations among measures of GAD clinical severity, generalized anxiety, and worry. Conclusions: These findings have important implications for evidence-based practice and interpreting studies seeking to compare clients from research and clinical settings on clinical characteristics.