Human, birds and other mammals can be infected by avian influenza A (H5N1) virus. Bird infections spread among continents in the last 2 years. Human infections become endemic in certain areas, characterized with young patients and high mortality. An unprecedented epizootic avian influenza A (H5N1) virus that is highly pathogenic has crossed the species barrier in Asia to cause many human fatalities and poses an increasing pandemic threat. This summary describes the features of human infection with influenza A (H5N1) in epidemiology and etiology and reviews recommendations for prevention.