Human monkeypox, occurring in the tropical rainforest of west and central Africa, is regarded as the most important orthopoxvirus infection for epidemiological surveillance during the post-smallpox era. This disease, first recognized in Zaïre in 1970 resembles smallpox clinically but differs epidemiologically. Clinical features, their evolution and sequelae of monkeypox could be compared with discrete ordinary or modified type of smallpox. A case-fatality rate of 14% has been observed but some cases can be exceedingly mild or atypical and may easily remain undetected and unreported. Pronounced lymphadenopathy has been the only clinical feature found commonly in monkeypox but not in smallpox. Fifty-seven cases of human monkeypox have occurred since 1970, in the tropical rainforests in six west and central African countries, the majority of them (45) being reported from Zaïre. The disease appears to be more frequent in dry season. Children below ten years of age comprise 84% of the cases. Smallpox vaccination protects against monkeypox. Clusters of cases have been observed in certain areas within countries and within affected households. Human-to-human spread has possibly occurred seven times. No cases of possible tertiary spread were observed. The secondary attack rate among susceptible close household contacts was 10%, among all susceptible contacts 5%. This is much lower than that occurring with smallpox, which is between 25-40%. The limited avidity of monkeypox virus for human beings indicates that monkeypox is probably a zoonosis, although the animal reservoir(s) have not yet been identified. The low transmissibility, resulting in low frequency of disease in man indicates that monkeypox is not a public health problem. Human monkeypox has been a relatively newly recognized disease. Studies are in progress to identify the natural cycle of monkeypox virus and to define better its clinical and epidemiological characteristics. Special surveillance is maintained in endemic areas with the aim to provide assurance that in spite of waning immunity of the human population following cessation of the smallpox vaccination, the disease does not constitute a potential danger to man.