Background: Pre-analytical errors are widely recognised as the most vulnerable step of the total testing process and can compromise patient safety through specimen rejection, delays and misleading results. This systematic review aimed to synthesise evidence on the prevalence, types and causes of pre-analytical errors in clinical laboratories. Methods: The review followed PRISMA 2020 guidelines. Electronic databases were searched for observational studies conducted in clinical laboratory settings that reported quantitative data on pre-analytical error rates, described specific error types and/or investigated contributing factors. Eligible full texts were screened against predefined criteria, and data were extracted on study characteristics, error definitions, overall error or rejection rates, distributions of error types and reported causes. Findings were summarised narratively because of heterogeneity in designs and outcome measures. Results: Seven cross-sectional or retrospective audits from hospital laboratories in different countries were included. Sample sizes ranged from 200 audited specimens to more than 300,000 samples and over 2 million tests. Across studies, pre-analytical errors represented the largest share of total laboratory errors or were the leading cause of sample rejection. Reported overall pre-analytical error or rejection rates varied from below 1% to more than 12%, while one quality-indicator audit found at least one pre-analytical defect in almost all samples. The most frequent error types were hemolysed and clotted samples, insufficient volume, use of inappropriate containers, delayed or non-received specimens, and incomplete or inaccurate request forms. Contributing factors included inadequate staff training, high workload, suboptimal phlebotomy practice, poor adherence to protocols and lack of harmonised quality indicators. Conclusion: Pre analytical errors remain highly prevalent across diverse clinical laboratory settings and are largely driven by preventable human and organisational factors. Targeted interventions combining continuous education, standardised procedures, robust informatics and routine monitoring of quality indicators are essential to reduce pre-analytical risk and strengthen patient safety.