<br><b>Introduction:</b> In 2021, the Central Center for Quality Research in Laboratory Diagnosticsconducted 26 tests as part of nine programs of external quality assessment of laboratorytest results, in which 1,475 Polish medical diagnostic laboratories (MLD) participated. The programs concerned the evaluation of the results of control determinations in the field ofclinical chemistry, hematology, coagulology and immunochemistry and were carried out withvarying frequency: four or two series of tests per year. Participation in the programs was freeof charge for MLD, but obligatory and financed by the Minister of Health.</br><br><b>Materials and methods:</b> Control materials from professional companies were used in theprograms, and courier mail was used to transport them to the MLD for fast and safe deliveryof samples.</br><br><b>Results:</b> Cumulative assessments of the results of control assays are presented in the form oftables and figures. The initial tables (IVIII) show summary studies of the results of all programsconducted in 2021. The following tables (IXXVII) present detailed data including the numberof evaluated results and the percentage of correct results according to the accepted evaluationcriteria obtained in individual programs with division by analytes.</br><br><b>Conclusions:</b> In the programs implemented in 2021, the percentage of correct resultsaccording to the most favorable criterion for the participant was slightly higher than in 2020(from 0.02% to 2.17%). Also, the annual regularity scores in the programs implementedin 2021, despite the ongoing SARS-CoV-2 coronavirus pandemic, were comparable to theresults assessed in 2020.</br>