Background : Birth weight is a powerful predictor of infant survival, growth, long-term healthrnand psychosocial development. Low birth weight has been defined by the World HealthrnOrganization (WHO) as weight at birth of less than 2,500 grams. Low birth weight (LBW) is arnrisk factor for infant mortality, morbidity, growth retardation, poor cognitive development andrnchronic diseases later in life.HIV infection during pregnancy may have a negative effect on birthrnweight, preterm birth and still birth.rnOBJECTIVE : the main objective of this study is to determine the effect of HIV infection onrnbirth outcome.rnMETHODOLOGY: Health facility based comparative cross sectional study was conducted torndetrmine the effect of HIV infection on birth outcomes. A pretested data collection form wasrnused to extract data from records of systematically selected pregnant women and their birthrnoutcomes. Data was entered and validated using Epi -Info 3.5.1 for windows. Statistical analysisrnwas performed using SPSS version 16 for windows. Bivariate analysis using studentâ€™s t-test wasrnperformed to compare means of continuous variables . Differences in proportions was analyzedrnusing the chi-square test . Ethical clearance was obtained from the ethical review committe of thernschool of public health(SPH) and institutional review board(IRB) of College of Health Science ofrnAddis Ababa University.rnRESULT: A total number of 711 pregnant women, 237 (33.3%) HIV infected and 474 (66.7%)rnHIV uninfected and their newborn characteristics was extracted from ANC and delivery registersrnand analyzed. The overall LBW rate was 11.7%% while mean birth weight was 2953+20.98(SE).rnMean birth weight tend to be lower in infants born to HIV infected women compared to HIVrnuninfected women (2724.78 + 41 grams VS 3064.55 + 22 grams , independent t test , P