Background: Although structured interviews are assumed to be scientifically superior to checklists for measuring youth psychopathology, few studies have tested this hypothesis. Interviews place a much greater burden on respondents, making it critical to determine their added value when quantifying psychiatric symptoms. Methods: Confirmatory factor analysis was used to compare interviews and checklists in community (N = 251) and clinically referred (N = 406) samples of youth aged 5 to 17 years. We examined the associations between mother-reported externalizing symptoms assessed by interview versus checklist against (a) teacher-reported externalizing symptoms, and (b) child's gender, academic performance, single- versus two-parent family, and family income. Models in which associations were estimated freely were contrasted to models in which the interview and the checklist were constrained to have equal associations with the variables. Finding these models fit comparably would suggest no difference between interviews and checklists. Results: In the community sample, both the constrained and unconstrained models provided comparable fit to the data, suggesting no marked differences between interviews and checklists. In the clinical sample, associations with the interview were generally stronger. Reducing the number of items on the interview to match those on the 6-item checklist eliminated these differences, suggesting that the increased reliability of the interview scales, afforded by additional items, enhanced their quantification of psychopathology. Conclusions: Consistent with previous studies, interviews were not notably superior to checklists for the measurement of externalizing symptoms. When only a few items are used, small performance differences between checklists and interviews may be due to scale length.