One of the many controversies concerning the borderline personality disorder (BPD) diagnosis is whether the construct refers to a categorical or dimensional variable. The current study used Meehl's (1973) maximum covariance analysis to investigate this issue. The charts of 409 psychiatric inpatients were systematically reviewed for the presence of BPD and dysthymic symptoms. Charts of 244 inpatients were also reviewed to assess the presence of indicators of male sex, a categorical variable. The results for BPD and dysthymia were consistent with a dimensional model, whereas those for male sex were consistent with a categorical model. A dimensional model of classification of BPD is recommended, and suggestions for future research are provided.