Biopsy of a cervical lymph node from a 3 1/2-year-old Caucasian boy originally was diagnosed as malignant lymphoma, lymphocytic type. Following therapy with radiation and prednisone, the patient had transient pancytopenia but was free of apparent disease for the subsequent 15 months. At age 5 he presented with fever, induration and congestion of the lower abdomen and scrotum, splenomegaly, abnormal liver function, hepatomegaly, lymphadenopathy and progressive pancytopenia. Biopsies of axillary and abdominal adipose tissue, cervical and axillary lymph nodes, liver and bone marrow were suggestive of, but not diagnostic of, malignant lymphoma. Despite therapy with prednisone, cyclophosphamide, and vincristine, the patient had continued fever and progressive hepatosplenomegaly and expired on the sixty-first hospital day. At autopsy there was no evidence of lymphocytic lymphoma but there was disseminated histiocytosis involving liver, spleen, bone marrow, lymph nodes, diaphragm and abdominal panniculus. In retrospect, occasional similar histiocytes were noted in lymph node sections from 2 years previously. The authors interpret this case as representative of disseminated lymphohistiocytosis, an apparently familial disease with distinctive clinicopathologic features.