The literature on borderline personality disorder (BPD), including its epidemiology, biology, phenomenology, causes, correlates, consequences, costs, treatments, and outcomes is vast. Thousands of articles and books have been published. Because the true prevalence of BPD by sex (gender) in the general population is still unknown, the important question of why women, rather than men, are more frequently diagnosed with BPD remains largely unanswered-despite current evidence for the origin of personality disorder in genetics and neurobiology, and despite recent suggestions that biased sampling is the most likely explanation for gender bias in the diagnosis of BPD. This paper reviews selected literature on (a) the epidemiology of BPD, (b) gender bias in the diagnosis of BPD, and (c) the social construction of diagnosis, particularly the diagnostic entity labeled "Borderline Personality Disorder." It attempts a synthesis of diverse, multidisciplinary literature to address the question of why women outnumber men by a ratio of 3:1 in the diagnosis of BPD. It rests on assumptions that (a) to varying degrees sociocultural factors inevitably play a role in the expression of disease conditions, and that (b) personality disorders, including BPD, have cultural histories. It also rests on the belief, for which there is considerable scholarly support, that the phenomenon called BPD has multiple, complex, interactive, biological, psychological, and constructed sociocultural determinants. Nurses must understand the phenomenon at this level of complexity to provide appropriate care.