Scrub typhus, a mite-transmitted zoonosis caused by Orientia tsutsugamushi, is a disease endemic to Taiwan. Serious complications in scrub typhus were more common in the past 4 years than reported previously. Between August 1993 and July 1997, 33 cases of scrub typhus were admitted at Tri-Service General Hospital. Symptoms and signs were: fever (100%), chills (39%), cough (24%), headache (21%), diarrhea (18%), dyspnea (18%), eschar (60%), adenopathy (33%), and rash (21%). Nineteen percent (6/32) had obvious leukopenia (WBC < 4000/ mm3), 34% (11/32) had leukocytosis(WBC > 10,000/mm3) and 44% (14/32) had thrombocytopenia (platelet count < 100,000/mm3). Elevation of aspartate aminotransferase (AST) and elevation of alanine aminotransferase (ALT) were 81% (26/32) and 75% (24/32), respectively. Serious complications included pneumonitis 36% (12/33), acute respiratory distress syndrome (ARDS) 15% (5/33), acute renal failure 9% (3/33), myocarditis 3% (1/33) and septic shock 3% (1/33). One patient died of ARDS due to delay in diagnosis. Other patients recovered after appropriate antibiotic and intensive supportive treatments. Emerging virulent strains of O. tsutsugamushi in Taiwan might be biologically plausible. Scrub typhus should be considered in a patient with fever, varying degree of respiratory distress, particularly if there is an eschar or a history of environmental exposure in endemic areas. Prompt diagnosis, timely antimicrobial therapy and intensive supportive care are important for ARDS and other life-threatening complications.