Objectives:To determine the prevalence and incidence of Human Immunodeficiency Virus type-1(HIV-1) infections and to describe change in the prevalence of Sexually Transmitted Infections (STI’s) and related risk sexual behaviours in a rural village, northeast, Tanzania.Design: A longitudinal study involving a total village population.Methods:Two survey rounds were conducted in 1991 and 1993 where the whole village population was invited to participate. A total of 3249(83.6%) individuals participated in 1991 and 2191 (76.9%) participated in 1993. Following written consent, all participants were tested for HIV-1 and those aged 15-44 gave specimen for STI’s and were further interviewed regarding their risk sexual behaviours.Results:The total prevalence of HIV-1 infections increased from 1.3% to 1.8% from 1991 to 1993. (p=0.17). Overall HIV-1 incidence in this rural population was 8.9/1000 Person-Years at Risk (PYAR), 13.0/1000 PYAR for women and 4.3/1000 PYAR for men. Relative Risk (RR) = 3.0; 95% CI: 1.12-8.16, p= 0.02). Married participants had a high incidence of HIV-1 than single participants (20.1/1000 PYAR vs. 7.0/1000 PYAR, RR=2.8; 95%CI 1.16-6.89, p=0.01). From 1991 to1993, the prevalence of gonorrhoea increased from 0.6% to 3.9% (p=0.00) with men more affected than women. In women, the prevalence of Bacterial Vaginosis (BV) rose significantly from 3.3% to 18.2% (p=0.00) and that of Vaginal candidiasis from 4.5% to 18.8% (p=0.00). Majority of respondents (98%) knew about HIV/AIDS transmission and about 90% of respondents reported having changed their risk sexual behaviours. However, 121 (38.2%) of men and 71(14.5%) of women (p=0.00) continued to involve themselves in multiple sexual liaisons with married participants at the highest risk. More men than women (6.8% vs. 2.2% in 1991, 6.6% vs. 1.1% in1993) reported to engage in casual sex during travel. The overall increase in condom use was modest. Conclusions:The rate of HIV-1 infections is at increase in this rural population coupled by an increase in the prevalence’s of other STI’s. Increase in risk sexual behaviours is the likely explanation for the increase in STI/HIV-1 infections. The acquired knowledge regarding HIV/AIDS has not been adequate to initiate desired behavioural change. More intensive HIV -1 control measures targeting high risk men and vulnerable women particularly those who are in marriages are needed.