Sarcomatoid carcinoma of the upper aerodigestive tract continues to be one of the most difficult diagnostic challenges for surgical pathologists. Histogenesis has been settled in favor of a divergent (mesenchymal) differentiation of a carcinoma, most often a squamous cell carcinoma. Finding the carcinoma and/or its immunohistochemical marker in the metaplastic cells establishes the diagnosis. There are, however, lesions that can simulate sarcomatoid carcinomas to varying degrees, and in which neither a definable carcinoma nor immunohistochemical evidence of one can be found. Such lesions fall into several categories: 1. benign reactive lesions, 2. inflammatory myofibroblastic tumors, 3. sarcomas, usually low-grade, 4. atypical pseudosarcomatous proliferation. The clinicopathologic considerations of sarcomatoid carcinomas are presented in this context and include immunohistochemical findings, prognostic factors, and biologic course.