This research evaluates the diagnostic efficacy of selected Child Behavior Checklist (CBCL; Achenbach & Rescorla, 2001) and Youth Self-Report (YSR; Achenbach & Rescorla, 2001) scales in an outpatient setting. One hundred and eighty-one children and adolescents ages 6 to 18 completed the CBCL and YSR measures with participants grouped according to their Axis I diagnosis. A board-certified psychiatrist, other than the researcher, assigned diagnoses. Results from positive predictive power (PPP), negative predictive power (NPP), sensitivity, specificity, and the area under the curve (AUC) showed no differences between youth diagnosed with single Axis I depressive disorders and depressed co-disordered or anxious youth. Depressed co-disordered and anxious youth obtained significant results on the CBCL Somatic Complaints (AUC = 0.632, p < .001), Withdrawn/Depressed (AUC = 0.594, p < .01), and YSR Externalizing (AUC = 0.619, p < .01) scales. Depressed co-disordered youth obtained high PPP rates, varying from 71% to 92% on the CBCL, and from 69% to 90% on the YSR. Sensitivity rates varied between 62% of correct classification with the CBCL Somatic Complaints scale, and 93% on the YSR Internalizing scale. Anxious youth obtained similar results with correct classification rates of 50% (PPP) for both CBCL and YSR scales. Diagnostic accuracy, that is sensitivity, reached 99% on the CBCL Externalizing scale, and 98% on the YSR Anxious/Depressed scale. These results indicated good diagnostic efficacy for the CBCL and YSR. Results further showed that symptom overlap and variations in symptoms negatively influenced the diagnostic efficacy of both CBCL and YSR in predicting Axis I disorders.