Rapid progress in molecular technologies has enabled the detection of several oncogenic viruses in various types of tumors. The pathogenesis of Hodgkin's disease is suggested to have a strong association with Epstein-Barr virus (EBV). However, Hodgkin's disease related to EBV shows a wide geographic variation in epidemiology. These variations among different populations suggest an interaction of environmental factors and a direct role of EBV infection. Therefore, we performed a comparative study on epidemiologic, histologic, and virologic features of Hodgkin's disease among those in the western part of Kenya and in Nagasaki, Japan. The age distribution of Hodgkin's disease showed a distinct peak in the 0-9-year-old age group in Kenya, and a higher and lower peak in the 60-69- and 30-39-year-old age groups, respectively, in Japan. The most common subtype of Hodgkin's disease in both countries was mixed cellularity, followed by nodular sclerosis, lymphocyte depletion, and lymphocyte predominance. Mixed cellularity showed a significantly high prevalence among Kenyan children nine years of age or younger. Using the in situ hybridization method, EBV-encoded RNA (EBER-1) was detected in 79% of the Kenyan cases and 59% of the Japanese cases, with the mixed cellularity subtype showing a strong correlation with EBER-1. There was 100% positivity in both countries in those less than nine years old. These results suggest that EBV plays a more direct role in the pathogenesis of Hodgkin's diseases in Kenya, especially in cases among young children and also in Japanese children. Environmental and/or genetic factors may have a role, in addition to EBV, in the pathogenesis of Hodgkin's disease, especially in Nagasaki, Japan.