Background: There is a need for dependable quality assessment (QA) of the widely used CoaguChek point-of-care testing prothrombin time monitor. By use of the prescribed set of 5 CoaguChek certified international normalized ratio (INR) QA plasmas, we compared the reliability of the immediate QA of individual monitors described in the European Community-recommended Technology Implementation Plan with conventional external QA analysis. Methods: Experienced staff tested CoaguChek point-of-care monitors in routine use for controlling oral anticoagulant dosage at 9 Netherlands Thrombosis Service Centres. Testing was performed with both the certified CoaguChek INR for a set of 5 QA individual plasmas from the Eur Con Action on Anticoag (ECAA) and conventional external QA analysis. Results: Patients brought 523 CoaguChek monitors to our service centers for assessment. The proportion with unsatisfactory performance indicated by a 15% deviation from the ECAA set was compared with 15% deviation from overall median INR of all CoaguChek monitors in the survey, as in conventional QA analysis. The results were similar (20.3% and 18.5%, respectively). Interlot differences of CoaguChek test strips were detected, but the incidence of unsatisfactory performance was similar with both analyses, from 6.5% to 37.5% with the certified INR method and from 5.9% to 33.3% with the overall median analysis. Conclusions: The results validate the use of the European Action on Anticoagulation rapid single-instrument QA-specific procedure for CoaguChek users compared with the nonspecific conventional QA analysis that relies on deviation from the overall median INR.