Kikuchi's histiocytic necrotizing lymphadenitis (Kikuchi's disease) is a histologically alarming but self-limiting lesion typically affecting the cervical lymph nodes of young adults. The authors report the first case of fatality occurring during the active phase of Kikuchi's disease. The 38-year-old patient presented with fever and generalized lymphadenopathy. During hospitalization, he developed abrupt onset of heart failure and died. Postmortem examination revealed enlarged lymph nodes all over the body showing typical histologic changes of Kikuchi's disease, but there was no encroachment on vital structures. The heart was dilated and flabby, with multiple microscopic foci of necrosis and mild fatty change. There were no other significant findings, and all cultures were negative. The authors speculate that large amounts of cytokines produced by the histiocytes or high endogenous catecholamines resulting from the stress response might be responsible for the myocardial damage. Alternatively, infection by an as yet uncharacterized microbial might be the underlying cause for both the lymphadenitis and myocardial disease.