The presence of skin involvement in breast cancer results in the classification of the tumor into the highest tumor category, and accordingly into the highest non-metastatic disease stage (current TNM classification: T4/stage III). This traditional view is no longer justifiable, as tumors that show non-inflammatory skin involvement (T4b) make up a considerably heterogeneous group with a high percentage of small-sized tumors. Classifying all lesions demonstrating this feature together results in the combination of tumors with widely differing prognostic and therapeutic implications into a single group. This violates the basic principle of the TNM concept in that only tumors exhibiting similar extension and prognosis should be grouped into one category/stage. Furthermore, the currently valid definitions of non-inflammatory skin involvement are misconceived for the substantial group of small tumors which often have ambiguous morphologic findings: the clinical classification depends on the subjective perception of the individual observer, and the pathologic staging considers histologic criteria that are not justifiable from a functional-morphological point of view. For these reasons, we strongly feel that there is a need to revise the current T4 category. We recommend that breast carcinomas currently classified as T4a-c should be eliminated from the T4 category and classified simply according to their tumor size (T1-3). The prognostically very unfavorable inflammatory carcinoma (T4d) should be maintained as the only clinicopathologic entity in the T4 category. This proposal, which will also lead to a revision of the stage III group, adheres more closely to the goals and principles of the TNM classification than do the current classification guidelines. Through the revision of the T4 category, the definitions and guidelines of inflammatory breast carcinoma should be adapted to the internationally accepted nomenclature.