The purpose of the current retrospective study was to determine the most sensitive and specific cutoff value of plasma D-dimer level associated with deep-vein thrombosis (DVT) after total hip (THA) or knee (TKA) joint arthroplasty. Diagnosis of DVT was determined by bilateral ascending venography pre- and postoperatively. Plasma D-dimer levels were measured by a latex photometric immunoassay system (LPIA) preoperatively and postoperatively on days 1, 3, 7, 10, 14, and 21. Postoperative DVT diagnosed by venography was found in 22 patients (40.1%) after THA and in 18 patients (64.3%) after TKA. Plasma D-dimer levels were significantly higher ( P < 0.01) in patients with DVT than in those without DVT on days 1, 7, and 10 after THA, but only on day 7 after TKA. Statistical analysis confirmed that a cutoff value of 10.0 microg/ml for D-dimer on day 7 was most sensitive (THA, 95.5%; TKA, 94.4%) and most specific (THA, 96.9%; TKA, 90.0%) in the diagnosis of DVT after THA as well as TKA. It was concluded that over 10 microg/ml of LPIA D-dimer on postoperative day 7 appears to be an indication of the occurrence of DVT after THA and TKA.