Persons infected with the Kaposi's sarcoma-associated herpesvirus (KSHV) are at risk for developing Kaposi's sarcoma (KS), but the risk factors for KSHV infection and for KS following infection are not well defined. Classical KS (cKS) occurs without apparent immune deficiency (such as AIDS or an allograft). The proposed study will test specific hypotheses and generate new hypotheses on the risk of cKS among persons who have antibodies against KSHV, on the risk of KSHV seropositivity, and on the risk of active KSHV infection, defined as KSHV viremia or viral shedding in saliva. To do so, 120 incident cases of cKS from throughout Sicily and approximately 1800 persons (15% KSHV seropositive) of similar age, sex, and community size will be asked to participate by providing questionnaire data and blood and saliva specimens. Residual formalin-fixed, paraffin embedded tissue from KS skin biopsies will be available for verification of diagnosis and molecular analyses. Primary hypotheses are focused on host genetic susceptibility, endogenous clinical conditions (such as asthma and allergy), and exogenous exposures (cigarette smoking and contact with certain plants, water and soil) that are postulated to affect KSHV activation, dissemination, and disease induction. The study will have sufficient statistical power to detect factors that increase the risk of KSHV seropositivity by 1.5- to 2-fold, the risk of cKS by 2- to 3-fold, and the risk of KSHV viremia or shedding by 3- to 4-fold.