Reflective functioning is a quantified index of mentalization, that is, an empirically based operationalization of the capacity to interpret one's own and others' behaviors in terms of mental states (Fonagy, 2008). The aim of this research was to examine the metric characteristics of the Reflective Functioning Questionnaire (RFQ-46) in adolescent sample. The study involved 194 high school students, of whom 81 (41.15%) were boys and 113 (58.75%) girls, whose age range is from 14 to 18 years. The study was conducted using the paper-pencil method during the school hour. First, the factor structure of the questionnaire was checked. Three factors were identified: Uncertainty/Confusion about Mental Conditions (NOM), Excessive Security in Mental Conditions of Others (ESM), and Interest /Curiosity about Mental Conditions (IOM), with reliability coefficients of .833 for the first factor, .779 for the second and .732 for the third factor. In order to check the diagnostic validity of the questionnaire, the correlation of individual factors, on the one side, and different measures of psychopathology, on the other, were examined. This was done by using the Borderline Personality Disorder Characteristics Scale for Children (BPFSC-11; Sharp et al., 2014), the Depression, Anxiety and Stress Scale (DASS- 21, Lovibond and Lovibond, 1995) and the Impulsivity subscale from the Hyperactivity-Impulsivity-Attention scale (Vulić-Prtorić, 2006). The NOM factor was shown to be significantly positively correlated with all the above psychopathology measures, and it was also shown that the participants whose score was above the cut-off value on the Personality Disorder Characteristics Questionnaire scores significantly higher results on the NOM factor compared to those which are below the cut-off limit. The ESM factor was positively correlated with borderline personality disorder, depression and impulsivity, while the IOM factor was negatively correlated with borderline personality disorder and depression. We can conclude that the examined factors have significant correlations with different measures of psychopathology. Therefore, it can be said that the diagnostic validity is confirmed. For the purpose of convergence-divergence validation, the association between these three factors and related constructs was examined: focused awareness was measured on the Focused Awareness Questionnaire (MAAS, Brown, & Ryan, 2003) and cognitive empathy was measured on the subscale Perspective-taking wich belongs to the Interpersonal Reactivity Index (IRI, Davis, 1983). The NOM factor shown to be negatively correlated with focused awareness but not related to perspective taking. The ESM factor, on the other hand, was positively correlated with perspective-taking but was not associated with focused awareness. The IOM factor was positively correlated with both constructs. Further analysis of results also pointed to gender differences in mentalisation, and it was found that girls achieved significantly higher average scores on the NOM and IOM factors than boys. Looking at the results of this research, it can be said that the metric characteristics of the Reflective Functioning Questionnaire are satisfactory, where the NOM factor, which has been most associated with different types of psychopathology, should be particularly emphasized. However, much research remains to be done to determine whether this measure can validly and reliably capture the various difficulties of mentalization that may be associated with psychopathology.