The aim of the study is to investigate how clinicians in psychiatric care for adults consider borderline personality disorder to be manifested in men and women, respectively. Could there be a tendency to over-diagnose women and under-diagnose men? In addition, the purpose of the study is to bring clarity to the reasons for gender differences within borderline personality as perceived by the clinicians. The study is based on an inductive approach, in which interviews have been conducted with twelve clinicians working with borderline personality disorders to gain a deeper understanding of how the clinicians consider the manifestations of gender differences. The clinicians described tendencies for women to deliberate self-harm, have mood swings and problems in relations. Men with borderline personality disorders are described as having a higher degree of e.g. aggressiveness, addiction and criminal behaviour than women with the same diagnosis. Half of the informants think men are under- diagnosed for borderline personality disorders. This may indicate that other diagnoses are given to men instead or that men end up in other treatments. Possible explanations to the gender differences are discussed, such as societal factors, gender roles or criteria for diagnosis based on gender.