The aim of this study was to assess tlte potential risk of trallsmission of HumanrnImmunodeficiency Virus type-i (HIV-i) by transfllsion of blood screened as negativernfor HIV antigen (Ag)/antibody (Ab) in the Ethiopian Red Cross Society-National BloodrnTransfllsioll Service (ERCS-NBTS) in Addis Ababa, Ethiopia. Assessment of riskrnfactors, test peljormance and efficiency of the HIV screening methods of the ERCSNBTSrnlaboratol)' (Ag/Ab EIA, Virol/ostika HIV Uni-Form II Ag/Ab) was made. A totalrnof 408 blood samples from unlinked one-time donations were collected and screenedrnfor HIV-i illfection by [{sing Roche Amplicor V i.5 DNA PCR and discrepallt res liltsrnwere checked by Westem blot alld HII' RNA assays. Data analysis was done by usingrnSTATA software. The cJ'llde prevalence of HI V-I illfection in blood do 1101'S as screenedrnby the ERSC-NBTS was 4.2%, while it was 3.4% as screened by nllcleic acid testillg.rnTitus, nucleic acid testillg methods detected 3 false positive samples. All HIV-infectedrndonors were replacement donors. The fourth-generation assay lIsed at ERCS-NBTSrnhad an excellent test agreement with HIV-i DNA PCR assay. The validity oftlte Ag/AbrnEIA was vel)' high as depicted by its: sensitivity (JOO%), specificity (99.2%), testrnefficiency (99.3%), positive predictive value (82.4%) and negative predictive valliern(J OO%). Although no false negative blood unit was detected, it was shown that aroundrn0.7% of the donated blood would be wrongly discarded as false positives. Tflis stlldyrnhas also provided good evidence for the need to introduce strong and improved dOllorrnselection criteria. This would include, minimizing or exclusion of replace men I dOllars,rnwith an emphasis on recruitment of regular vohmtm), do 1101'S, and ellllcation of bothrndOllors and the general public on tlte need for safe blood. Similar studies should berndone in other parts of the co/Inti)' before drawing a general conclusion abollt thernquality/safety of blood donatiolls in Ethiopia. Fllrther stlldies all HIV incidence amongrnblood donors, propel' estilllation of risk of HIV transmission through transfllsion, andrnprevalence of HII' infection in transjilsion recipients are essential for monitoring thernsafety of the blood supply. Studies on other transjilsion transmittable infectiolls agentsrnshollld also be IIndertake//.