Empathy is understood as a multidimensional construct involving both cognitive and emotional factors for which, traditionally, gender differences have been reported. The Interpersonal Reactivity Index (Davis in Catalog Sel Documents Psychol 10:1-19, 1980) is an instrument made up of four subscales, each measuring a different dimension of the global concept of empathy. Attending to gender differences, the present study's objective is twofold. First, it aims to determine, conceptually speaking, whether or not the model analyzed by this instrument is equivalent for the two sexes. Second, it aims to determine which dimensions involved in empathy most strongly predict gender differences. The results convey that the proposed model is invariant between boys and girls, although the dimensions exhibited significant differences of magnitude as a function of sex. Mainly two variables (Considerate Social Style and Impassiveness) were capable of distinguishing between men and women. Possible reasons for these results are also discussed.