Leptospirosis is a potentially serious but treatable zoonotic disease, representing a worldwide public health hazard. Its symptoms may mimic those of a number of other unrelated infections such as influenza, meningitis, hepatitis, dengue or viral hemorrhagic fevers. It is important to distinguish leptospirosis from these diseases. For this reason, new diagnostic methods have been developed in recent years. In humid tropical and subtropical areas, where most developing countries are located, leptospirosis poses a greater health problem than in areas with a temperate climate. Because leptospirosis is easily overlooked and consequently underreported in many parts of the world, it is necessary to increase awareness and knowledge of the disease as a public health threat. The aim of these guidelines is to assist in this process. The target groups to which these guidelines are directed consist of health workers, clinicians, laboratory technicians, microbiologists, public health workers, veterinarians and biologists with an interest in zoonoses, having no specialized knowledge of leptospirosis, but who wish to be generally informed about the microorganism concerned and the disease that it may cause. This is not a handbook and avoids technical details, but the interested reader can find further information in the annexes and the general bibliography. These guidelines are concerned essentially with human leptospirosis.World Health Organisation Staff is the author of 'Human Leptospirosis: Guidance for Diagnosis, Surveillance and Control', published 2003 under ISBN 9789241545891 and ISBN 9241545895.