Background: This study describes the development of the Brief Child and Family Phone Interview (BCFPI)--a computer-assisted telephone interview which adapts the revised Ontario Child Health Study's (OCHS-R) parent, teacher, and youth self-report scales for administration as intake screening and treatment outcome measures in children's mental health services. It focuses on the factor structure of the BCFPI's hypothesized parent-reported child mental health scales describing attention-deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), conduct disorder (CD), separation anxiety disorder (SAD), generalized anxiety disorder (GAD), and major depression (MDD). Methods: Data for the analysis come from an OCHS-R measurement study that included two groups of children and adolescents selected from the same urban area: a general population sample (n = 1,712) and a clinic-referred sample (n = 1,512); and a third sample that was enlisted in a province-wide implementation study of clinic-referred 6- to 18-year-olds (n = 56,825). We used confirmatory factor analysis to assess the factor structure of the BCFPI scales in different populations and to test measurement equivalence across selected groups. Results: Despite the strong constraints imposed on the measurement models, estimates of model fit across the three samples were comparable in magnitude and approached the cut-offs suggested for the GFI and CFI (greater than 0.9) and RMSEA (less than 0.05). Measurement equivalence was demonstrated between the OCHS-R clinic and provincial implementation samples. Within the implementation sample, the factor structure of the BCFPI scales was equivalent for boys versus girls and for 6- to 12- versus 13- to 18-year-olds. A companion paper examines the test-retest reliability, sensitivity, specificity, and validity of these BCFPI scales when used for screening. Conclusion: This project supports the feasibility and acceptability of a computer-assisted telephone interview for assessing emotional-behavioral problems of children and adolescents referred to children's mental health services.