Background: The worldwide incidence of childhood cancer is increasing and has become the leading cause of disease-related mortality in the developed countries. In high-income countries, more than 80% of children with cancer are cured, but in many low and middle-income countries only 20% are cured, including Ethiopia. Delay in diagnosis and treatment of cancer patients may impact on poor prognosis and quality of life. In this study delay as classified in factors related to the patient and health care systems.rnObjective: The aim of this study was to assess factors influencing delay to diagnosis and initiation of treatment among pediatric oncology patients attending at black lion specialized hospital oncology unit, Addis Ababa, Ethiopia, 2019.rnMethods: This study was an institutional based cross-sectional study conducted on 244 pediatric cancer patients from February to April, 2019. Data was collected using structured questionnaire from parents or caregiver of the children through interview and supported from medical reviews. Bivariate and multivariate analysis using Odds ratio (OR) was utilized to evaluate association between dependent and independent variables. All statistical analysis was performed using STATA (Version 14), and statistical significance was set at P < 0.05.rnResult: In this study 244 children participated in which the response rate was 100%. The mean age of child was 6.4 years (SD Â± 3.2). With regards to prevalence of delay, 127(52.0%) were patient delay (> 30 days) and 104(42.6%) were having health system delay (>30 days). Factors that were the predictor of patient delay include: age, place of residence, diagnosis of the child and visit to traditional hillers showed significantly associated (P