Self-report, when available, is considered the ideal way to assess the intensity and other aspects of pain in children. However, self-report scales are often too complex cognitively for preschool-aged children (2-4 years). The Rainbow Pain Scale (RPS) was developed to provide individualized self-reported pain ratings for preschool-aged children. The psychometric properties of this scale have yet to be evaluated. To ensure validity, our first step was to compare RPS scores to a well-validated scale in older children who were able to self-report their pain. The purpose of this study was to assess the concurrent validity of the RPS in children aged 5 to 10 years as proof of principle. We compared ratings of 49 children's pain using the RPS with those on the Faces Pain Scale-Revised (FPS-R). Participants suffering from pain related to cancer and cancer treatment were recruited to complete both scales at 3 time points, during both inpatient and outpatient clinic visits. Pearson's r and Cohen's κ were used to evaluate the level of association between the scales. The association between RPS and the FPS-R was greater than .7 at all 3 visits; r = .96 between the scales at the first clinic visit, .97 at the second visit, and .93 at the third visit. Cohen's κ between scales was 1.0 at the first clinic visit, .95 at the second visit, and .87 at the third visit. The RPS shows excellent concurrent validity with the FPS-R in school-aged children. The next step will be to examine the psychometric properties of the RPS in preschool-aged children.