The need for a self-report instrument that assesses internalizing problems in children ages 8 through 12 is evidenced in the lack of such an instrument, and in the prevalence of internalizing problems in children. A new self-report instrument, the Internalizing Symptoms Scale for Children (ISSC), has been proposed and developed to fit this need. The present study evaluated the criterion-related validity, clinical cutoff points, and discriminating power of the ISSC. Two groups of child subjects, clinic-referred and general-school-population, were recruited and administered the ISSC, and a parent of each subject completed the Child Behavior Checklist (CBCL). Each case within the clinic-referred group was then classified as an Internalizer or non-Internalizer based on the CBCL Internalizing T-score. The CBCL was identified as the criterion because of empirical methods used in creating the factor structure, extensive clinical use, psychometric properties, cross-informant design, and large research representation. Results of the evaluations indicated the ISSC to have moderate, yet adequate evidence of criterion-related validity, an optimum clinical cutoff point of 70 (raw score), and strong discriminating power. These results give support for the clinical use of the ISSC as a screening instrument, and for potential use in diagnosis and treatment planning.