BACKGROUND Because early recognition and initiation of antibiotic therapy are important, clinicians should familiarize themselves with the clinical presentation of leptospirosis, and determine prognostic factors. METHODS This study included all patients treated at Angers University Hospital between January 1995 and December 2005 for leptospirosis - both probable (cases combining epidemiologically suggestive features with compatible clinical, laboratory, and radiographic findings, with no other diagnosis envisioned) and confirmed (by finding microorganism on direct examination or culture of blood, urine or CSF, or by seroconversion or by a significant increase in the antibody titer between two samples). Severe leptospirosis was defined by hospitalization in the critical care department or need for renal dialysis. The statistical analysis used SPSS software version 12. RESULTS Of 97 records reviewed, we retained 62 cases that met the criteria above, including 35 confirmed cases, 27 probable and 15 severe. The sex ratio was nine men for every woman. The patients' mean age was 45+/-18 years [12-77]. The principal clinical signs observed were: fever (n=59) with shivering (n=42), diffuse myalgia (n=41), headaches (n=38), jaundice (n=24), conjunctival suffusion (n=10), rash (n=11), herpes eruption (n=7), renal damage (n=33) that was sometimes severe (>500 micromol/L) (n=7), meningitis (n=12), meningoencephalitis (n=2), myocarditis or pericarditis (n=6), and atypical radiographic lung disease (n=16), sometimes with ARDS (n=6). Blood tests showed thrombocytopenia (platelets<140 G/L) in 65.5% of patients (n=40). Logistic regression modeling showed that two criteria remained independently predictive of development toward severe leptospirosis: clinical jaundice (p=0.005) and cardiac damage seen either clinically or on ECG (p<0.02). These factors can be identified easily at the first clinical examination and during evolution, and should help to reduce mortality by allowing earlier management of patients with suspected leptospirosis.