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.