Because the epidemiology of viral hemorrhagic fever is unclear, each outbreak is a spectacular event that focuses the attention of the international scientific community. When an epidemic of Marburg virus disease occurred in the Durba region located in the northeastern part of the People's Republic of the Congo, 23 scientists were sent from 12 different countries. Sixty of the 73 people infected died. The first case was observed in December 1998 and the last in May 1999. Because of political unrest in the country, the outbreak was not reported immediately and most data was collected by observers retrospectively. However Marburg virus infection was confirmed in 5 of 16 patients in whom testing was performed and person-to-person transmission was demonstrated. Thus the Durba outbreak was the first epidemic of Marburg virus disease not involving laboratory contamination. Initial epidemiologic findings suggest that the first cases involved miners who were probably infected by contact with an animal reservoir such as bats. Further studies to determine seroprevalence in the general population and virologic testing on animals captured in the zone should provide answers to these questions.