The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) is a widely used instrument to assess obsessive-compulsive symptomatology. The present study provides evidence that the Y-BOCS is best represented by a three-dimensional model comprising severity of obsessions (factor 1), severity of compulsions (factor 2) and resistance to symptoms (factor 3). On the basis of exploratory factor analysis, this structure was found for both baseline (n = 109) and discharge ratings (n = 68) following a multimodal cognitive-behavioral intervention. The factor solution remained essentially unchanged when two optional items (items 1b and 6b) were dropped from analysis. The three-factor structure was replicated with confirmatory factor analysis and showed better fit than previously proposed single- and two-factor models. For future research, we propose a new Y-BOCS scoring algorithm that takes this factor structure into account. A further result was that resistance significantly declined in response to cognitive-behavioral intervention, whereas drug treatment alone did not seem to moderate this variable according to previous research conducted by Kim et al. [Psychiatry Research 51 (1994) 203-211].