Among 111 patients referred to our outpatient clinic for isolated thrombocytopenia during a 24-month period, 17 (15.3%) cases of EDTA-dependent pseudothrombocytopenia (EDTA-PTCP) were identified. EDTA-PTCP represented the second most frequent cause of thrombocytopenia in this population. The diagnosis was confirmed by the following findings: (a) normal platelet numbers immediately after blood withdrawal; (b) progressive fall of platelet counts and evident platelet clumping over time, only in EDTA-anticoagulated blood. A simple, inexpensive and quick diagnostic method was devised, that consists in evaluating the platelet number in a blood sample anticoagulated with EDTA immediately after blood withdrawal and 4 h later.