Background: Evaluated five probability indices, including odds ratios, to determine relative contribution of Uncontrollable Excessive Worry (DSM-IV criterion A and criterion B) and Physiological Symptoms associated with uncontrollable excessive worry (DSM-IV criterion C) for diagnosing DSM-IV generalized anxiety disorder in youth. Method: One hundred eleven youths (6 to 17 years old) and their parents who presented to a childhood anxiety disorders specialty clinic were administered a semi-structured diagnostic interview schedule. Separate evaluations were conducted for children and adolescents. Results: Results showed that symptoms comprising DSM-IV's generalized anxiety disorder diagnosis vary relative to one another in the degree to which they contribute to the diagnosis, with certain symptoms having relatively higher diagnostic value than other symptoms. The relative value of symptoms also appeared to vary with children's and adolescents' reports, and parents' reports about their children and adolescents. Conclusions: Despite variations in symptoms' values, with only a few exceptions, almost all symptoms were still quite useful for diagnosis, whether reported by children, adolescents, or their parents.