Background and objectives: Clinical laboratories play an enormous role in appropriate and reliable medical decision making, given that a large proportion (70-80%) of diagnoses are based on laboratory tests. To ensure reliability of patient Results and avoid reporting of erroneous Results, quality indicators detecting laboratory errors are required. “Laboratory error” is defined as any defect in the testing process, with a reported frequency of 0.012-0.6%. Total testing proces in the laboratory comprises of three phases: the pre-analytical phase, analytical and post-analytical phase. This study aimed to identify reasons for rejection of biological specimens at Dr George Mukhari tertiary laboratory. Objectives was to identigy and classify the causes of biological specimen rejection, to identify areas where improvement is necessary, as well as to advise on preventative strategies.    Methods: This was a retrospective study conducted in the department of Chemical Pathology at Dr George Mukhari Academic Hospital, Pretoria, South Africa. Data regarding specimen rejection were extracted from the laboratory information system from January to December 2019. Results: From a total of 2463572 specimens received during the study period, 81687 were rejected, Resultsing in a rejection rate of 3.3%. The rejection rate per laboratory was as follows: chemistry, 54%, haematology, 25%, virology, 13%, microbiology, 8%, and cytology, 0.15%. The main reasons for rejection were old specimens, wrong specimens, and haemolysis, accounting for 30%, 15% and 13% respectively. Community health centres showed the highest number of rejected specimens (30%), with the least (2%) from the paediatric outpatients department. Conclusions: Sample integrity was found to be the major reason for samples being rejected; this included old samples, haemolysed samples, followed by incorrect samples and insufficient samples received by the laboratory. The highest number of rejected samples was from the community health centres, suggesting a need for improvement in specimen handling and transportation from these sites.