Back groundrnSexually Transmitted infections (STIs) are among the most common causes of illnesses in the rnworld and their public health importance is high in developing countries. They are therncommonest causes of healthy life years lost among women of 15-49 years in Africa. InrnEthiopia,there is little information regarding the incidence and prevalence of STIs. According tornFederal HIV/AIDS prevention and control office report of 2006, adult prevalence of syphilisrn2.7% was only known. Similarly, study on the level of knowledge and STI service utilizationrnpattern involving the whole reporductive age group in the community at large is minimal. rnObjective : This study was conducted to determine the level of knowledge and servicernutilization for common STIs among 15-49 years of adult women and men in Shakiso District. rnMethodsrnA cross sectional community based descriptive study was conducted using interviewer rnadministered questionnaire in Shakiso District on a sample of 845 adult women and men selectedrnfor study through multistage sampling technique. In this study the quantitative part wasrnsumplemented with a qualitative study. With regard to measurement of knowledge level on STIs,rnscoring system of each knowledge question was considered. The STI magnitude was estimatedrnfrom self reported STIs symptoms. A pre tested questionnaire was filled by trained datarncollectors and checked on daily basis for completeness and consistency. The data was analyzedrnusing SPSS version 16 soft ware and descriptive, bivariate and multivariate analysis were made.rnHere logestic regression model was used to determine independent predictor of outcomernvariables. rnResult: A total of 845 participants [385(45.6%) males and,460(54.4%) females] were includedrnin the study with a mean age of 27.7(SD=8.2). Of 784 (92.7%) who heard of common STIs, onlyrn20.8% (63.8% of males,36.2% of females) of them had good comprehensive knowledge (COR=rn2.24;95%CI,1.57-3.2). In a multivariate analysis having good comprehensive knowledge wasrnassociated with formal education at all level (P-value â‰¤ 0.002 ). Self reported magnitude of STIsrnsymptoms ranged from 4.6-6.9%. Having history of premarital sexual intercourse was rnstatistically significant with occurrence of self reported STIs syndromes according to rnmultivariate logestic regressions (Adjusted OR 2.5;95%CI=1.46-4.3). Most respondents (96.7%)rnhave got treatment for STIs. Qualitative and quantitative findings revealed that, fear ofrnquarreling with partners, failure to get cure easily,stigma and affordability (lack of money)rnrelated issues were factors or barriers for STIs service utilization. rnConclusion: Low level of comprehensive knowledge on STIs and increament of STIs magnitudernin comparison to other studies in the country were identified in the study rnRecommendation: IEC and BCC strategies should be considered as top priority to creaternawareness among communities inorder to prevent and control STIs transmission.