Two weeks after rafting on a river in Thailand a Dutch 54-year-old male experienced chills and high fever. While rafting he had wounded his hand. Because of the history (water contact, the wound, high fever with chills), of the findings at examination (fever, conjunctivitis) and of the laboratory findings (leukocytosis, albuminuria, disturbance of liver enzymes), a clinical diagnosis of 'leptospirosis' was made. This was confirmed by serological tests and culturing of Leptospirae from the blood. Leptospirosis is a zoonosis, in man associated with certain occupations, water sports and inundations. The clinical picture varies from a mild febrile disease (sometimes pyrexia of unknown origin) to a severe condition with kidney and liver failure, bleeding tendency, lung oedema (Weil's syndrome). In travellers with fever, water contact, leukocytosis and neutrophilia, leptospirosis must be considered and specific diagnostic tests applied.