A rare case of metastatic malignant melanoma of unknown primary origin in a 49-year-old woman is reported. The swelling, localized in the right inguinal region, was partially immovable and associated with progressively increasing pain. Initial diagnosis was set by needle aspiration cytology and was confirmed postoperatively by histologic examination of a surgical specimen. Cytomorphologic features of metastatic malignant melanomas are described and the difficulties of identification discussed. A brief review of the literature is also made, and the rarity of the case and the value of cytologic diagnosis are emphasized.