Pulmonary manifestations in leptospirosis are considered a major complication and are related to a poor prognosis. We present a large series of patients with pulmonary involvement using a practical approach based on the presence of acute respiratory failure (ARF).A retrospective study of patients with confirmed leptospirosis.One hundred and sixty-nine patients with a laboratory-confirmed diagnosis of leptospirosis were investigated. One hundred and thirty-four patients (36.7±14 years of age) had pulmonary involvement. Severe pulmonary involvement was defined by evidence of ARF. Univariate analysis found the following factors related to severe pulmonary leptospirosis: dyspnoea (OR=10.14, p<0.0001), pulmonary crepitations (OR=4.8, p<0.0004), abnormal chest X-ray (OR=9.88, p<0.007) with alveolar shadowing (OR=8.12, p<0.0001), oliguria/anuria (OR=5.48, p<0.0001), hepatomegaly (OR=7.11, p< 0.0001), shock (OR=8.38, p< 0.0001), ICU admission (OR=60.08, p< 0.0001), dialysis (OR=4.87, p< 0.001), mechanical ventilation (OR=216, p< 0.0001) and development of nosocomial infection (OR=21.5, p< 0.0001). The mortality rate was significantly different between severe (40%) and non-severe (5.3%) pulmonary forms (OR=11.87, p< 0.0001). Multivariate analysis found two independent factors related to severe pulmonary involvement: dyspnoea (OR=10.18, p< 0.0001) and oliguria/anuria (OR=4.87, p< 0.0009). We performed a multivariate analysis to assess independent factors related to mortality and found: mechanical ventilation requirement (OR=27.85, p< 0.0001) and AST greater than 150 IU/L (OR=4.57, p< 0.02). Haemoptysis was associated with survival (OR=0.2, p< 0.02).Severe pulmonary involvement in leptospirosis is associated with extensive disease involving other organs. The association of multiple factors is associated with severe forms of the disease and a high mortality rate.