Lymphangioleiomyomatosis (LAM) is an uncommon progressive disease characterized by a hamartomatous tumor-like proliferation of smooth muscle cells that occurs most often in women. This disease commonly involves the lymph nodes, lungs, and mediastinum, and rarely the abdominal sites. We report a case of mesenteric LAM occurring in a 37-year-old man affected by Klinefelter syndrome with a 17-year history of androgen replacement therapy. Histology revealed a hamartomatous proliferation of spindle cells surrounding multiple ectatic lymphatic spaces intermixed with lymphatic follicles. When subjected to immunohistochemical studies, the tumor cells stained positive for muscular markers and negative for estrogen, progesterone, and androgen receptors. The occurrence of LAM in association with Klinefelter syndrome has never been reported in the literature and could represent a further clue in the still unclear pathogenesis of this disease.