Background: Tumor lysis syndrome (TLS) is a life-threatening emergency disorder,rncaused by an abrupt release of intracellular metabolites after tumor cell death. It isrncharacterized by a series of metabolic manifestations, especially hyperuricemia,rnhyperkalemia, hyperphosphatemia and hypocalcemia.rnObjective: The aim of the present study was to evaluate and characterize the incidence ofrntumor lysis syndrome in pediatric oncology patients before and after treatment in TikurrnAnbessa Specialized Hospital (TASH), Addis Ababa, Ethiopia.rnMaterials and Methods: Hospital based prospective cohort study was conducted in 61rnnewly diagnosed and admitted pediatric oncology patients in TASH in six moth duration.rnPurposive and convenient sampling technique was employed for the selection of healthrnfacility and study participants respectively. Socio-demographic data was collected byrninterview administered questionnaire. The patients were followed and the physicalrndiagnosis, imaging and laboratory results were interpreted by senior physicians. Datarnwas entered to and analyzed by SPSS version 23.rnResults: Out of 61 pediatric oncology patients 39(63.9%) were males. The mean (+SD)rnage of the pediatric patients was 6.39 (+3.67) years ranging from 2 months to 14 years.rnTotal of 29.5% of patients were found to have TLS. There were 11.5% and 18.0% ofrnlaboratory TLS (LTLS) and clinical TLS (CTLS) cases respectively. There were 72.2%rnspontaneous and 27.8% treatment induced TLS. There was 23% and 21.3% cases ofrnhyperuricemia and 4.9% and 6.6% cases of hyperkalemia incidence before and afterrntreatment respectively. Overall two patients died, in the study period, because of TLS.rnConclusion: The pediatric oncology patients in this study had a high incidence of TLS.rnTLS occurred irrespective of socio-demographic variability in the study participants.rnThis suggests that every child with cancer is at a risk of developing TLS. As TLS is a life-rnthreatening complication of malignancies, early identification of patients at risk andrnreducing morbidity and mortality is of crucial importance.rnKey words: tumor lysis syndrome, pediatric oncology, metabolic derangement, cell deat