Background: A Meta analysis of all randomized controlled trials showed that insecticide treatedrnnet use has an overall protective efficacy against all -causes of child mortality and malaria diseasernepisodes of 18% and 50%, respectively. Frequent washing, lack of retreatment, inconsistent use,rnother social and technical factors were shown to influence efficacy of bednets at field trials. Torndate, however, experience with local factors influencing the effectiveness of ITN programsrnremains very limited and it is not known whether the impact of treated nets in the context of wellrncontrolled randomized trials can be replicated under program conditions in all set-ups.rnObjective: To assess the effectiveness and influencing factors of ITNs in preventing clinicalrnmalaria in under five children in Aletawondo Woreda, Sidama Zone, SNNPR.rnMethods: A community based retrospective cohort study was conducted on a sample of 342rnunder five children (171 exposed and 171 unexposed/comparison group) residing in ChuckornTown & surrounding rural kebeles where there was ITN distribution. A precoded, pretestedrnstructured questionnaire was employed to obtain the necessary information after getting bothrnwritten and verbal consent from the concerned bodies. The collected data was daily checked forrncompleteness and consistency and it was entered into computer database. An internal comparisonrnwas also conducted to assess factors influencing effectiveness of bednets among those withrnhistory of malaria (cases) and without history of the disease within the exposed cohort. Otherrnappropriate statistical tests were done and interpretations were made accordingly.rnResult: The history of malaria attack from September to December 2004 among reported regularrnITNs users was 43.5% less than in those who didn't use/own bednet. This was statisticallyrnsignificant (OR=0.565 95%CI 0.346-0.925 p=0.023). The household factors that were foundrnto influence the effectiveness of ITNs were large family size, keeping livestock inside livingrnroom, using a bednet obtained a year or more, absence of retreatment of the bednet for more thanrn12 months, presence of hole/tears in the bednet, frequently washing the bednet and reportedrnhistory of rolling out of the child from the bednet during night time.rnConclusions & Recommendations: Despite lots of programmatic deficiencies, ITNs arerneffective in preventing clinical malaria in under-five children. Based on these,rnappropriate recommendations are forwarded.rnKey Words: (Clinical malaria, Under -five child, Insecticide treated mosquito netrnuse, Effectiveness, retrospective cohort, nested case control Design,rnInfluencing household factor)