OBJECTIVES: Recent clinical trials on the new anti-thrombotic agents have shown that the incidence of symptomatic deep venous thrombosis (DVT) and pulmonary embolism (PE) in patients undergoing hip or knee replacement ranges between 0.5 and 2%. This study aimed at assessing the real life incidence of DVT/PE after major orthopaedic surgery in Belgian and the impact of these complications on the length of stay based on a hospital disease database. METHODS: The incidence of DVT/PE and the average length of stay (LOS) among patients hospitalized for hip or knee replacement surgery were estimated using the longitudinal IMS Hospital Disease Database (year 2007), including data on 34.3% of Belgian hospital beds. Stays were searched based on ICD-9-CM codes corresponding to hip replacement (81.51-81.52-81.53) and knee replacement (81.54-81.55). Occurrence of DVT/PE was identified with ICD-9 codes 451.1-451.2-453.4. It was also checked whether selected patients were administered low-molecular-weight heparin (LMWH). The impact of a DVT/PE complication on LOS was assessed through a Wilcoxon non-parametrical test. RESULTS: A total of 9377 stays with hip replacement and 6,978 stays with knee replacement were retrieved in the database. More than 99.9% of the patients were administered LMWH in both subgroups. The number of stays with a DVT/PE episode was respectively equal to 51 and 75 within the 2 subgroups, resulting in an incidence of 0.54% in patients with hip replacement and 1.07% in patients with knee replacement. LOS of patients with a DVT/PE episode was more than twice as high after both hip (34.2 vs. 15.9 days; p<0.001) and knee (24.9 vs. 12.0 days; p<0.001) replacement. CONCLUSIONS: The incidences of symptomatic DVT and PE reported in clinical trials could be confirmed based on this retrospective search. The occurrence of DVT/PE doubles LOS in patients undergoing hip or knee surgery.