We retrospectively reviewed 34 consecutive patients with serologically confirmed leptospirosis admitted during years 1992-2002. Nine patients (26.5%) had respiratory symptoms on admission including cough (n = 4), shortness of breath (n = 4), cyanosis (n = 2), and hemoptysis (n = 1). Six patients had pulmonary radiographic findings including (1) diffuse, ill-defined, ground-glass density (n = 3); (2) diffuse alveolar opacities (n = 2); and (3) small nodular density (n = 1). Male/female ratio was 8/1 and mean age was 47 years. Seven patients reported their exposure source including hunting (n = 2), fishing (n = 2), fresh water swimming (n = 2), and canoeing (n = 1). All patients had fever (mean = 40.1 degrees C). Other common symptoms were headache (n = 4), vomiting (n = 3), and myalgia (n = 3). Biological abnormalities included elevated liver enzymes (n = 8), proteinuria (n = 7), lymphopenia (n = 6), hematuria (n = 5), renal failure (n = 4), anemia (n = 4), and elevated neutrophil count (n = 4). PaO(2 )was measured for 3 patients while they were breathing room air (32, 55, and 66 mmHg). Suspected diagnosis on admission included leptospirosis (n = 2), bacterial pneumonia (n = 2), intoxication, influenza, viral hepatitis, biliary tract lithiasis, and rapidly progressive glomerulonephritis (one patient each). The first serologic testing for leptospirosis was positive for 5 patients (55%). Serovar was presumptively identified for 7 patients: Australis (n = 3), Grippotyphosa (n = 2), and Icterohaemorrhagiae (n = 2). Seven patients were treated with penicillin; two patients received no antibiotics. All patients were cured. In conclusion, patients with leptospirosis may present predominantly with nonspecific pulmonary symptoms. In these patients, leptospirosis must be suspected when there is a potential exposure to rats, especially in case of high-grade fever, myalgia, hepatitis, and renal abnormalities.