Summary. Background: Closure time (CT), measured by platelet function analyzer (PFA-100®) device, is now available to the clinical laboratory as a possible alternative or supplement to the bleeding time test. Aim: On behalf of the Platelet Physiology Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH-SSC), a working Group was formed to review and make recommendations on the use of the PFA-100 CT in the evaluation of platelet function within the clinical laboratory. Methods: The Medline database was searched to review the published information on the PFA-100 CT in the evaluation of platelet disorders and platelet function. This information, and expert opinion, was used to prepare a report and generate consensus recommendations. Results: Although the PFA-100 CT is abnormal in some forms of platelet disorders, the test does not have sufficient sensitivity or specificity to be used as a screening tool for platelet disorders. A role of the PFA-100 CT in therapeutic monitoring of platelet function remains to be established. Conclusions: The PFA-100 closure time should be considered optional in the evaluation of platelet disorders and function, and its use in therapeutic monitoring of platelet function is currently best restricted to research studies and prospective clinical trials.