Researchers have been striving to explore the function ing of patients with borderline personality disorder from the perspective of their capacity to mentalize. Analyzing the expanding body of literature, it is nevertheless difficult to reach a clear conclusion. There are studies that con firm mentalization deficits in this group; however, there are also reports suggesting better or at last equal mental izing in borderline individuals compared to controls. This paper discusses a hypothetical explanation of these con tradictory results by analyzing three fundamental issues. It is assumed that: (1) different aspects of mentalization are measured in studies-some of them are disordered, while others remain intact in borderline individuals; (2) mentali zation can be understood not only as a trait but also as a state, and its level may differ in the same person depend ing on measurement conditions; (3) the borderline group is heterogeneous in terms of mentalizing because other varia bles determine the level of this capacity.