Epidemiological data were collected on the slow virus disease, kuru, among the Fore cultural and linguistic group in Papua New Guinea from 65 kuru patients who died or were diagnosed between 1977 and 1981. From these, 3 episodes of cannibalistic feasts were identified, in each of which 2 or more participants were exposed to the infectious agent for the first time and died within weeks or months of each other 25–30 years later. Thus, it is shown that the natural incubation period of kuru could be as long as 25–30 years and is at times identical in 2 or more individuals infected at the same time, even over this span of years; also it is not determined by age at exposure. Further analysis of the episodes supports the concept on which the study was based, namely the transmission of kuru at the time of cannibalistic mourning with primary infection often occurring in infancy or early childh