In a prospective study of 4,840 patients, we determined the annual incidence of clinical deep vein thrombosis (DVT) in mobilized, discharged orthopedic-operated "high-risk" patients (hip replacement surgery, knee replacement surgery, nailed hip fracture) and assumed "low-risk" patients (diagnostic knee arthroscopy). In addition, the time from the operation to the time when the patients were readmitted with clinically suspected DVT and the distribution of radiologically-confirmed DVT were recorded. Thromboprophylaxis was routinely given for about 10 days to the high-risk groups during the hospital stay but not to patients undergoing knee arthroscopy. During 9 years, the annual incidence of DVT following major procedures was 2.1% (95% CI 1.6-2.6) vs. 0.6% (95% CI 0.2-1.1) after diagnostic knee arthroscopy. Symptoms appeared, on average, 27 (3-150) days after total hip replacement surgery, 36 (3-150) days after nailed hip fracture, 17 (6-30) days after total knee replacement and 1 (1-6) day after knee arthroscopy. In hip-operated patients, 50% of the DVT's were found in the proximal veins vs. 40% following knee arthroplasty.