Clinical aspects of 10 consecutive patients hospitalized for acute human leptospirosis, confirmed by serology using the microscopic agglutination test (MAT), between 1975 and 1988 in a 1000 beds Teaching Hospital are retrospectively analyzed. All of them were male, mean age of 55, presenting a suggestive epidemiological data to be at risk for Leptospira infection. Leptospira icterohaemorrhagiae was responsible for 8 cases and Leptospira canicola for 2. 7 patients were treated, after 3-4 days of admittance, with penicillin. 5 patients died. Cause of death was gastrointestinal haemorrhage in 3 and cardiogenic shock in 2. We discuss the clinical, biochemical, pathological and therapeutic aspects of the acute human leptospirosis.