Monoclonal extramedullary plasmacytoma (EMP) is a rare, low-grade lymphoma found predominantly in the head and neck region. Only since the introduction of immunophenotyping techniques 2 decades ago has it been possible to differentiate EMP from benign polyclonal plasma cell proliferation. The purpose of this study was to trace the evolutionary profile of the disease under consideration of monoclonality assessment. The records of 24 patients with morphologically diagnosed EMP treated in a single institution underwent clinical and pathological review. Only 14 patients had true monoclonal plasmacytoma. No EMP-related deaths occurred. Two patients had local recurrence, and 2 patients developed multiple myeloma. Review of the literature confirms the low-grade malignancy of EMP. Diagnostic procedures must exclude benign polyclonal plasmacytoma, multiple myeloma, and solitary bone plasmacytoma. The slow natural progression of the disease and the rarity of secondary multiple myeloma favor nonmutilating local surgery whenever possible to avoid the long-term sequelae of radiotherapy.