Kaposi's sarcoma (KS) has become a source of interest in recent years primarily for its strong association with the acquired immune deficiency syndrome (AIDS). Endothelial cells (EC) are central to inflammation and can regulate coagulation and leucocyte emigration and may be central to the development of the disease. As they are also capable of being infected by HIV in vivo, this infection may contribute to the immunosuppressive effects of HIV seen in AIDS. Recent work has shed new light on the mechanisms involved in EC proliferation. The aim of this article is to review such evidence implicating EC in the development of KS. Additionally, hypotheses will be put forward to explain the mechanism of the vascular proliferation in KS and the possible role of EC in HIV infection. There is therefore enormous potential for the therapeutic targeting of endothelium to control these diseases.