In view of the threat of use of the variola virus as a biological weapon, the interest of medical and other public in this causative agent that was eradicated in the wild at the end of the 1970s has increased. The paper gives an outline of the current knowledge on biological properties of the variola virus, and on the epidemiology, pathogenesis, clinical picture and prophylaxis of the disease caused by this virus. Descriptions of two sudden smallpox epidemics (Germany in 1970 and former Yugoslavia in 1972) could illustrate the potential of the smallpox virus as a biological weapon in bioterrorism and biological warfare. In fact, this virus can spread very readily through aerosol, which may lead to explosive epidemics. Not having been immunised, our population aged less than 25 years totally lacks the immunity. Older individuals are likely to have a low residual specific immunity to the agent. The only way to prevent a smallpox epidemic is by vaccination and patient isolation. A rapid smallpox diagnostics and prompt vaccination of all contacts is of utmost importance in stopping the outbreak.