The structure and magnitude of sex differences in interpersonal problems across several data sets were examined, guided by the interpersonal circumplex model and the structural summary method. Data were self-reported interpersonal difficulties, assessed with the 64-item version of the Inventory of Interpersonal Problems (IIP; L. M. Horowitz, S. E. Rosenberg, B. A. Baer, G. Ureno, & V. S. Villasenor, 1988). In Study 1, the authors focused on sex differences at the level of specific interpersonal complaints (item level). In Study 2, the authors examined sex differences in octant scores of the IIP circumplex (scale level), in a reanalysis of archival data. The structural summary method was used to identify points of maximum difference between men and women in the interpersonal continuum and to estimate effect sizes. Results from the 2 studies converged in suggesting a dimension of difference involving problems in Hostile-Dominance vs. Friendly-Submission. The magnitude of effect size was consistent with previous reports in the personality literature. These sex differences appeared to be best explained by a one-dimensional model. Findings were generally consistent across 3 different types of samples. (Contains 6 footnotes, 3 tables, and 7 figures.)