The aim of this study was to evaluate the structure of DSM-IV borderline personality disorder (BPD) criteria. The study group consisted of 564 consecutively admitted inpatients and outpatients. BPD criteria discriminatory power was tested by using corrected item-to-total and item-to-diagnosis correlations. Weighted least-squares (WLS) confirmatory factor analysis (CFA) was used to assess the fit of DSM-IV BPD unidimensional model. The categorical model of BPD was tested by exploratory latent class analysis (LCA). Item analysis suggested a hierarchy in BPD criteria discriminatory power, even if with different rank order with respect to the DSM-IV model. CFA showed a unifactorial structure with congeneric items as the best fitting model for DSM-IV BPD criteria (chi2 = 18.89, df= 27, P > .87). LCA showed evidence for three latent classes; heterogeneity was observed only among subjects falling below DSM-IV diagnostic threshold for BPD. These results support the categorical model of BPD, even if with several differences with respect to DSM-IV.