To extend the epidemiological study on adult T-cell leukemia-lymphoma (ATL) in japan, the geographical and demographic characteristics of carriers of human T-lymphotropic virus type I (HTLV-I) and patients with ATL were analyzed in Tsushima Island, which is one of the typical endemic areas of ATL in Kyushu, japan. Even on the small island of Tsushima (710 km2; pop. 48,875; 123 villages), the positive rates of anti-HTLV-1 antibody among the 58 villages studied varied from 2% to 50%, a fact that is probably associated with the historical events affecting the movement of the indigenous population of Tsushima Island. The positive rate of anti-HTLV-1 antibody in males increased little with age; however, the female rate increased distinctly with age in moderate and high HTLV-1-endemic villages where more than 15% of the inhabitants had positive anti-HTLV-1 antibody. Analysis of anti-HTLV-1 antibody positivity between spouses confirmed that HTLV-1 was more contagious from husband to wife than from wife to husband, which corresponded to the fact that the positive rate of anti-HTLV-1 antibody in females older than 30 years was higher than that in males. Recently the rate of carrier children from HTLV-1 carrier mothers was estimated at around 20%. The recent annual incidence rates of ATL among 1,000 HTLV-1 carriers older than 40 years living in Tsushima Island was estimated at 2.2 in males, 0.8 in females.