OBJECTIVE: The incidence of post-operative venous thromboembolism (VTE) events - deep vein thrombosis (DVT) and pulmonary embolism (PE)- is traditionally thought to be low in Asia and the routine use of thromboprophylaxis remains controversial. The primary objective of the AIDA study was to assess the incidence of DVT after orthopedic surgery without prophylaxis. The pharmacoeconomic part aimed to estimate the cost of illness of VTE in the six Asian participating countries (Indonesia, Korea, Malaysia, Philippines, Taiwan and Thailand). METHODS: Patients who underwent major orthopedic surgery in 8 study hospitals had a post-operative bilateral venography. All direct medical costs associated with the management of DVT and/or PE including hospitalization, medications, laboratory tests, procedures and clinic visits were recorded and adjusted to 2002 USD. Costs were determined from the hospital perspective. RESULTS: A total of 407 patients were enrolled in the study. In the interim analysis, based on 103 patients who completed the 3-month follow-up, 47 patients had a radiological DVT according to the local evaluation. In Indonesia, Korea and Malaysia, hospitalization stay appeared to be the major cost driver constituting 37.2%, 63.7% and 63.1% of the overall cost, respectively. A higher percentage was spent on medications to treat DVT in the Philippines (77.7%) than in other countries. Four cases of PE were identified in Korea, Thailand and Taiwan. The cost of PE represented a major part of the overall VTE cost in Thailand and Taiwan, increasing by three-fold compared to DVT costs. CONCLUSION: Distribution of cost items amongst countries greatly varied depending on the healthcare system and medical care (no/no no). In some countries, significant amount of resources were consumed by patients who developed DVT or PE, the no-prophylaxis strategy therefore could have the potential of incurring extra healthcare cost.