Six penitentiary institutions from Asunción and border cities were visited in order to determined the seroprevalence of HIV and syphilis infection. Six (0.9 percent) out of 663 sample from the prison inmates were positive for HIV-antibodies and 20 (3 percent) were VDRL reactive. These results show that HIV is already present in this population as well as syphilis, which may be a coto factor in the HIV propagation. Our findings underline the urgency of education programs in order to reduce the risk of HIV infection in closed closinstitutions such as prisons