The Reflective Functioning Questionnaire for Youths (RFQY) is a self-report measure of reflective functioning (RF) also referred to as mentalizing. Lower levels of RF are characteristic of a wide range of mental disorders and are especially relevant in the assessment of personality pathology. The goal of the current study is to examine the psychometric properties of a Danish translation of the RFQY and to corroborate previous research on the measure's ability to differentiate between adolescents with and without borderline personality disorder (BPD) features. 889 adolescents were administered the RFQY and divided into three subsamples: a community sample (n = 644), a clinical non-personality disorder sample (n = 64), and a BPD sample (n = 181). Construct validity was examined through bivariate correlations between RFQY and a dimensional assessment of borderline personality features. Analysis of variance (ANOVA) supported the utility of the RFQY to discriminate between adolescents with and without BPD features. Moreover, a two-factor structure based on previous research of the adult version of the RFQ was examined. A series of exploratory and confirmatory factor analyses yielded a two-factor structure corroborating previous research. Implications for prevention, assessment, and treatment are discussed along with methodological limitations and suggestions for future research.