This study targeted to assess knowledge, attitude and behavior (KAB) on HIV/AlDS/STDsrnamong workers in the informal sector in Addis Ababa. The study is based on the sample ofrnJ J 77 respondents.rnThe eli gibi li ty criterion for the selection of respondents is based on the definition of workersrnin the Informal Sector as adapted from CSA and MOLSA survey.rnThis work discusses the sampling procedure employed and the quality of data and examinesrnthe relationship between knowledge, attitude and behavior and selected backgroundrncharacteristics using univariate, bi-variate, and multipl-variate statistical techniques of datarnanalysis. In multi- variate analysis, logistic regression model has been employed.rnThe dependent variables were tested against the independent variables: age, marital status,rnplace of work and sample area and sex were used as useful variable.rnThe findings indicate that there is a positive relation between knowledge aboutrnHIV/AIDS/STDs and educational level. In self-reported STD infection, rel atively high raternwas exhibited with increase in educational level. Education by itself doesn't guarantee forrnbehavioral change. Males were more infected by STD than females . Attitude towards therndisease was found to be lower for females than males. Misconception in the mode of AIDSrntransmission was higher in the study population.rnThe study has found that the youth, working in the core business area and outside home needrntarget oriented intervention.rnFinally, the study concluded by suggesting recommendations, general and specific, that mayrnhelp to enhance awareness, attitudinal and behavioral change among the study population.