We have considered trends in the incidence of Kaposi sarcoma (KS) between 1978 and 2002, using data from the Swiss Cancer Registries of Vaud and Neuchatel (786000 inhabitants). Overall, 163 cases were registered, 149 in men and 14 in women. After a peak reached in 1988-1992 in both men (2.71/100000, world-standard) and women (0.26/100000), a considerable decline was observed thereafter, to reach 0.80/100000 men and 0.06/100000 women in 1998-2002. In men, there was a substantial decline (from 4.91/100000 in 1988-1992 to 0.56 in 1998-2002) at age 15-44 years, a fall from 2.91 in 1993-1997 to 2.37 in 1998-2002 at age 45-64 years, but some increases over the last decade in the elderly, likely due to cases of classic KS. The declines in KS confirm that earlier anti-retroviral therapies (HAART) had already reduced the risk of KS, and the newest highly active anti-retroviral therapies have further contributed to the decline of KS in recent years. [authors]