Primary plasmacytomas of the female genital tract are extremely rare and present a substantial diagnostic challenge. Five cases morphologically representing plasmacytomas and localized to the uterine cervix have been reported previously; however, only 1 was shown to be monotypic for immunoglobulin light-chain expression. We report the case of a 37-year-old woman who had highly atypical plasma cells on her Papanicolaou test. A clinically detected endocervical polyp was removed and revealed a plasmacytoma, the diagnosis of which was substantiated by demonstrating monotypic lambda-light-chain restriction and a clonal immunoglobulin heavy-chain gene rearrangement. The cytologic and histopathologic findings of plasmacytomas of the uterine cervix are discussed, including the utility of immunophenotypic and molecular techniques to confirm the neoplastic diagnosis.