Sinus histiocytosis with massive cervical lymphadenopathy (SHML) was originally described in 1969 as a benign clinicopathologic entity characterized by massive bilateral cervical lymphadenopathy, fever, leukocytosis, elevated ESR, and hypergammaglobulinemia, usually occurring within the first two decades of life. We present an illustrated case of an elderly patient with polyclonal hypergammaglobulinemia and a 2-year history of multilobulated cervical and submandibular lymphadenopathy. The etiology and pathogenesis of SHML are not known. Diagnosis requires lymph node biopsy to exclude other causes of cervical lymphadenopathy such as malignant lymphoma, malignant histiocytosis, metastatic carcinoma, and tuberculous lymphadenitis. Histologic examination shows marked dilatation of subcapsular and medullary lymph node sinuses containing large, foamy or vacuolated histiocytes. Although no curative treatment is known, corticosteroids, radiation therapy, vinblastine and oral cyclophosphamide, and surgery have been used to palliate constitutional symptoms and mechanical obstruction from massive lymphadenopathy. Since one third of SHML patients have evidence of disease for 5 years, and a mortality rate of 7% exists with benign histologic disease, all patients with SHML should be carefully screened for evidence of immunodeficiencies that may precipitate a fatal outcome.