Low achei vements in the Expanded Programme onrnImmunization (EPI) has been found to be one of the majorrnhealth problems in the North-Eastern Arsi region ofrnEthiopia. This study was conducted to assess fact orsrnhaving influence on the attainment of EPI rates at thernlevel of individual health care units. The factorsrnstudied were categorized as follows: a) Factors relatedrnto the health workers' knowledge, attitude and practice.rnb) Factors related to the the health care deliveryrnsystem, with emphasis on the provision of EPI service. c)rnFactors related to the char acteristics of the health carernuni ts, and d) factors related to the socio-cul tural,rndemographic and other characteristics of mothers. Twornhealth workers from each one of the 17 health care unitsrnwere included in the study population and from the arearnserviced by each health care unit, 50 mothers of undertwornchildren were selected . The study found that thernimmunization coverage rates attained by the individualrnhealth care units ranged from 18% to 96%. In the case ofrnpregnant women the rate ranged from 12% to 96%. The meanrnimmunization rates were 52.8% and 51% in the under-twornchildren and pregnant mothers, respectively. otherrnfindings were that daily EPI session, using occasions ofrnmass meetings or other public gatherings for informingrnthe public about EPI, weekly tracing of EPI defaulters,rnvirnand involving the community in EPI activities were foundrnto be associated with high coverage. Mothers'rneducational status, attitude towards the health carernsystem, and EPI, were positively associated withrnimmunization coverage.