The aim of this investigation was to analyse the HBV and HIV epidemiological pattern in Monte Negro rural zone, Rondônia State, Brazil. 925 inhabitants (randomly sampled) were studied, 496 (53,5%) were males and 429 (46,5%) were females. This sample represents about 7% of the whole Monte Negro county and 12% of the rural population. In the present research was observed that 10,35% were infected by HBV and that 58,73% had acquired the B hepatitis virus infection already. The high prevalence of HBsAg between sons matched with high prevalence of anti ? HBC between parents characterize the horizontal and domestic transmission. The vertical transmission in Monte Negro rural zone it is possible, but is as rare event. The findings point out for news investigations to elucidate the exact transmission mechanism. 923 inhabitants (randomly sampled) were analyzed for the presence of antibodies against HIV I and II, but no positive case were found. The local heath system has notified three positives cases, a woman identified in a prenatal consultation, other a rural worker (male) that probably acquired the infection during blood transfusion in Rondônia State and the third case an ex- presidiary wife that probably acquired HIV by heterosexual transmission. The findings point out an initial picture HIV infection on Monte Negro county, with a low epidemiological impact but that can rise as a great public health problem if not managed adequately.