Clinical laboratories provide essential information not only for diagnosis and monitoring, but also for screening, prevention, early diagnosis and tailored treatment. Physicians rely on accurate and timely laboratory test results to make appropriate decisions to provide effective patient care, as much as 60-70% of diagnoses depend on laboratory findings. The entire testing process in laboratory medicine includes every step in the cycle, starting with the clinician's decision to request a test, through the collection of samples, usually venous blood, to the receipt of the results by the initial requester. According to the definition of the International Organization for Standardization (ISO), a laboratory error is defined as a deficiency that occurs in any part of the laboratory cycle, from the search, analysis, reporting of results, to their appropriate interpretation and reaction to them. In recent years, it has been known that only 7% - 13% of errors in the overall testing process occur in the analytical phase. Most errors occur in the pre-analytical phase (46% - 68%), a phase that is usually beyond the control of the laboratory and includes sample collection (phlebotomy, venipuncture). The conducted research analyzed the pre-analytical errors of the samples submitted to the Institute for Medical Laboratory Diagnostics from the Clinic for Children's Diseases, Surgery, Internal Diseases and Children's Surgery of the Split Clinical Hospital Center before and after the education. The training was conducted by licensed employees of Hospitalija trade Ltd, the official distributor of Becton Dickinson. The obtained data are consistent with the results of other research on the number and type of pre-analytical errors and emphasize the importance of continuous education of health personnel.