This clinic-based cross sectional study aimed to assess the risky sexual behavior changes in the number of sexual partners after HIV counseling and testing among adults in Kilimanjaro Region in Tanzania in 2008.The study used a structured questionnaire to collect demographic data among 90 clients at three Voluntary Counseling and Testing (VCT) sites in Moshi Municipality, Kilimanjaro Region. The mean age was 33.5(±9.6). Sexually active respondents were 66.7 %. Overall, 81.1% reported multiple sexual partnerships [mean (SD): 3.8 ± 1.3]. Males were more likely to report multiple sexual partners than females (OR) = 3.8 [95% CI 1.5- 9.8]; P < 0.005). Males’ mean number of lifetime sexual partners before VCT was 1.5 and 1.1 after VCT, which decreased significantly (f= 3.6; p = 0.014).The mean number of sexual partners in the past 3 months before VCT was 1.5 and 1.1 after VCT, which decreased significantly (f=113.7; p = 0.000). The mean number of those who reported sex in the past 3 months was 1.6 before VCT and 1.1 after VCT, which decreased significantly (f= 5.9; p = 0.019). Females’ mean number of sexual partners in the past 3 months before VCT was 1.2 and 1.1 after VCT, which decreased significantly (f= 2.9; p = 0.000). The mean number of casual sexual partners was 1.3 before VCT and 1.1 after VCT, which decreased significantly (f= 4.7; p = 0.022). In conclusion, most participants are sexually active and practice multiple sexual partnerships; more VCT screening efforts and awareness are needed to reduce number of sexual partners among at high-risk people in Tanzania.