The Virus Research Laboratory of the University of Ibadan, Nigeria, was notified on 23 October 1969 that cases of suspected yellow fever had occurred in the Jos area. The diagnosis was confirmed by virus isolation and the existence of a widespread outbreak on the Jos Plateau and adjacent areas was established. This was the first recognized epidemic of yellow fever in Nigeria since 1953. Between September and the end of December 1969, an estimated total of 252 patients with yellow fever were hospitalized. The case-fatality ratio for hospitalized patients was approximately 40%. The diagnosis of yellow fever was confirmed by virus isolation, serology, or pathology in 55 patients. It is estimated that up to 100 000 cases of yellow fever may have occurred during the epidemic.