Introduction: Laboratory testing is an integral part of the clinical decision-making process,rnand results of laboratory testing often strongly influence medical diagnoses and therapies.rnQuality of specimen is an important factor that affects the accuracy and usefulness ofrnlaboratory results. The problem is high in resource poor countries like our country, Ethiopia.rnIdentifying the types, frequency and associated factors influencing the quality of clinicalrnsamples is important for designing appropriate interventions to prevent their generationrnand Serology departments. Compared with the respective frequency with which they collectrnthe specimen, laboratory personnel had significantly fewer rejected specimens thanrnNonlaboratory personnel. The proportion of specimens that were rejected in emergencyrndepartment and inpatient services were twice more than for the outpatient services.rnConclusion: Our finding shows the problems of specimens in the preanalytic phase and thernfactors involved in rejection of specimens, particularly with respect to specimen collectionsrnperformed outside the laboratory walls by Nonlaboratory personnel who are not under therndirect control of the laboratory; moreover, the finding shows that the rates of specimenrnrejection are higher for inpatients and ED than outpatients, owing to the performance ofrnoutpatient procedures by personnel under direct laboratory control.rnrnand hence improving the quality of laboratory service. Different literatures showed thatrnmore than 70% of errors in the laboratory occur in the pre analytical phase.rnObjective: The purpose of the study is to determine the frequency of specimen rejectionrnand associated factors of specimens submitted for different tests to the St. Paul hospitalrnmillennium medical college, Addis Ababa, Ethiopia.rnMethods: Cross sectional study design was applied at St. Paul hospital millennium medicalrncollege medical laboratory. A total of 8063 specimens were collected during the studyrnperiod. The quality of all specimens submitted to laboratory during data collection periodrnwere checked and inappropriate specimens were recorded in data collection checklistrnformat. The data was entered and analyzed using SPSS version 16.0 software.rnResult: Of 8063 total specimens submitted for testing to the laboratory of St. Paul hospitalrnmillennium medical college during the data collection period, 116(1.4%) were rejected. Thernmost frequent reason for rejection was hemolysis of specimen, which occurred much morernfrequently than the second most cited reasons, clotted specimens and unlabelledrnspecimens. Compared with their respective frequency of rejection of specimens by type ofrnrequested laboratory service, significantly more rejected specimens occurred in Hematolog