A case of fulminant leptospirosis is presented, manifesting as rapid progression from acute undfferentiated febrile illness to refractory shock, jaundice, renal failure and massive pulmonary hemorrhage. The patient received aggressive intensive care unit support including prolonged intubation and ventilation. This case emphasizes that acute leptospirosis may well not be characterized by the classic scenario of a biphasic illness, but rather by a fulminant, monophasic illness. © 2005 by The Brazilian Journal of Infectious Diseases and Contexto Publishing. All rights reserved.