objective: To describe clinical and laboratory features of patients with severe ehrilichiosis, some of whom presented with toxic shock syndrome (TSS)-like illnesses, and to report, to our knowledge, the first documented fatal case of ehrlichiosis in a child. design: Case series. setting: Tertiary-care medical center. patients: All patients with documented ehrlichiosis during a 3-year period, August 1, 1989, to July 31, 1992. results: Eight patients (age range: 2 to 46 years) met clinical and serologic diagnostic criteria for ehrlichiosis. The mean interval from first contact with a physician to initiation of appropriate antibiotic therapy was 4.6 days (range: 1 to 11 days). All eight patients with ehrlichiosis had fever, chills, thrombocytopenia, and abnormal liver function test results. Most patients also had rash (seven), conjunctival hemorrhage or erythema (six), and leukopenia (six). Four cases met diagnostic criteria for TSS with fever, hypotension, rash, and multiorgan dysfunction. Two patients required mechanical ventilation, and one of these, a 6 1 2-year-old boy, died of complications of the infection. A nineth patient with probable ehrlichiosis also met diagnostic criteria for TSS. conclusions: Human ehrlichiosis can present as a severe, life-threatening illness that may resemble TSS. The diagnosis of ehrlichiosis was not considered by the physicians who first cared for these patients. Greater awareness of the potential severity of ehrlichiosis is needed to ensure that proper treatment is initiated early in the course of the disease.