Two apparently immunocompetent adult patients developed acute fulminant hepatitis during presumptive primary herpes simplex virus type 1 (HSV-1) infection without any visible mucocutaneous lesions. HSV hepatitis was not suspected in the case of patient 1, who died without treatment. Patient 2 was empirically treated with acyclovir because of the triad of high fever, leukopenia, and markedly elevated levels of aminotransferases, and this patient survived. Most immunocompetent patients with fulminant HSV hepatitis do not have visible mucocutaneous ulcers, and HSV is frequently not considered as a cause of acute hepatitis. In summary, fulminant hepatitis can occur during HSV infections, the diagnosis is frequently missed or delayed because of the absence of mucocutaneous ulcerations, and patients who receive early empirical treatment with acyclovir can survive this illness.