Three patients with hyperthyroidism due to deliberate intake of excessive amounts of L-thyroxine are described wherein death was "instantaneous" and presumably due to ventricular fibrillation. Hyperthyroidism was not recognized on admission in two of these patients because of atypical presentations. Autopsy was performed in two patients. In one patient no coronary disease was present and focal myocarditis with leukocytic infiltration was noted. The second patient had an acute posterior myocardial infarction due to acute coronary thrombosis, but focal areas of leukocytic infiltration and fibrosis were also seen in the anterior wall not involved in the process of infarction. Factitious hyperthyroidism due to L-thyroxine abuse can be associated with sudden death in the absence of coronary artery disease and may be related to a drug induced myocarditis.