Pulmonary embolism (PE) is diagnosed with increasing frequency nowadays due to advances in the diagnostic methods and the increased awareness of the disease. There is a tendency to use non invasive diagnostic methods for all diseases. D-dimer is a fibrin degradation product. We aimed to detect the relationship between disease severity and the D-dimer levels measured with two different methods. We compared D-dimer levels in cases of massive vs. non-massive PE. A total of 89 patients who were diagnosed between 2006 and 2008 were included in the study. Group 1 included patients whose D-dimer levels were measured with the immunoturbidimetric polyclonal antibody method (D-dimerPLUS (R)), while Group 2 patients made use of the immunoturbidimetric monoclonal antibody method (InnovanceD-DIMER (R)). In each group, the D-dimer levels of those with massive and non-massive PE were compared, using the Mann Whitney U test. The mean age of Group 1 (25F/26M) was 56.0 +/- 17.9 years, and that of Group 2 (22F/16M) was 52.9 +/- 17.9 years. There was no statistical difference in gender and mean age between the two groups (p > 0.05). In Group 1, the mean D-dimer level of massive cases (n = 7) was 1444.9 +/- 657.9 mu g/L and that of non-massive PE (n = 34) was 1304.7 +/- 350.5 mu g/L (p > 0.05). In Group 2, the mean D-dimer level of massive cases (n = 6) was 9.7 +/- 2.2 mg/L and that of non-massive PE (n = 32) was 5.9 +/- 1.3 mg/L (p < 0.05). The mean D-dimer levels of massive cases as measured with the immunoturbidimetric monoclonal antibody method were significantly higher. Pulmonary embolism patients whose D-dimer levels are higher (especially higher than 6.6 mg/L) should be considered as possibly having massive embolism. Diagnostic procedures and management can be planned according to this finding.