Objectives:
The aim of the research was to determine the reliability, factor structure, as well as validity of the Mentalization Scale (MentS) – a self-report measure of mentalization.

Methods:
Two groups of subjects were examined. The first group (N = 202) consisted of students from Poznan universities; the other group (N = 229) consisted of individuals employed in various positions, with different education levels. The following measures were used: Mentalization Questionnaire, the Borderline Personality Inventory, the Experiences in Close Relationships Scale-Revised, the short version of the International Personality Item Pool NEO Personality Inventory, short version of Empathy Quotient and the Trait Emotional Intelligence Questionnaire.

Results:
Reliability analysis showed high internal consistency of all three MentS subscales, and the factor analysis supports the three-factor structure of the questionnaire. Mentalization as measured by MentS was positively linked with mentalization-related constructs: empathy and emotional intelligence. Obtained relations between mentalization and attachment dimensions, borderline features and personality traits as well as observed gender differences also support the validity of the MentS.

Conclusions:
The verification of the hypotheses formulated in the present study has led to the conclusion that the Polish version of the Mentalization Scale (MentS) – a new measure of mentalization – has high psychometric value and may be used for brief yet multifaceted measurement of mentalization.