Ebola virus was recovered from a nine-year-old girl who died of acute hemorrhagic fever in June 1977 at Tandala Hospital in northwestern Zaire, in the first reported recognized case of this disease since the discovery epidemics of 1976 in Zaire and Sudan. Investigations undertaken in the Tandala region revealed that two previous clinical infections with Ebola virus had occurred in 1972 and that about 7% of the residents had immunofluorescent antibodies to the virus. Females younger than 30 years of age had a higher prevalence of antibodies than males of comparable age, but above the age of 30 years there was no sex difference. No other clues to the still-mysterious natural reservoir of Ebola virus were uncovered.