The histological age determination of venous thromboses in fatal pulmonary embolism cases is an important task of forensic medicine and requires thorough knowledge of the general and specific pathology of pulmonary thromboembolism (PTE). The aim of our investigation was to carry out a chronological evaluation of the deep venous thrombosis (DVT) phenomenon, to assess the chronological transformation of the thrombus and to determine the causal relationship with PTE as cause of death. The clinical data and the autopsy records of the 2843 autopsies performed over the period 1 November 1998 to 31 December 2007 were retrospectively evaluated, and 140 cases in which PTE was pointed out as cause of death were selected. The dissection of the deep veins of the legs has been performed systematically to search for the starting point of venous embolism. 4.5% of pulmonary embolisms originated in the in iliac veins, 20.7% in the femoral veins, and 74.8% in the deep crural veins. In the venous sites of thrombosis, the histological assessment has been performed in conjunction with the surrounding vascular wall of uncut blood vessel with at least three to six different transverse incisions. Histological assessment of the embolus samples was also performed in conjunction with the venous sites of thrombosis. In our selected 140 cases of PTE, the DVT was classified as phase 1 in 48 cases (34.29%), as phase 2 in 70 cases (50%), and 22 cases (15.71%) were evaluated as older than 2 months (phase 3). The observed transformation of the thrombus by organization is suitable for a forensically utilizable age determination. However, only three chronological stages can be distinguished with any degree of certainty using immunohistochemistry and CLSM.