The first human cases of infections with entire avian influenza strain were caused by subtype A/H5N1/ and occurred in 1997 in Hong Kong. Since this year until 27 March 2007 World Health Organization confirmed over 370 human cases of infections with avian influenza and almost 160 persons died due to this pathogen. At present there is known that person to person transmission of avian influenza virus is limited. Nevertheless, it is possible that with time virus will adapt to human sufficiently to be able to cause next influenza pandemic. Despite intensive studies and global influenza surveillance there is no possible to predict when pandemic will begin and what kind of virus will cause this outbreak.