Venous thromboembolism, including deep-vein thrombosis and pulmonary embolism, is a major source of morbidity and mortality among elderly patients. To improve our understanding of elderly patients with deep-vein thrombosis, we compared 1932 patients with deep-vein thrombosis aged 70 years or older with 2554 nonelderly patients in a prospective registry of consecutive ultrasound-confirmed deep-vein thrombosis patients. The mean age of elderly patients was 78.9 +/- 6.1 years compared with 51.8 +/- 12.9 years in nonelderly (P < .0001). Elderly patients were more likely to have prior recent hospitalization (49.2% vs 44.7%, P = .03), congestive heart failure (20.5% vs 9.9%, P < .0001), chronic obstructive pulmonary disease (18.2% vs 11.7%, P < .0001), and recent immobilization (50.5% vs 39.6%, P < .0001) than the nonelderly patients. Elderly patients were less likely to present with typical deep-vein thrombosis symptoms of extremity discomfort (44.4% vs 60.6%, P < .0001) and difficulty ambulating (8.4% vs 11.2%, P = .002). Only 41% of elderly patients subsequently diagnosed with deep-vein thrombosis had received any venous thromboembolism prophylaxis. In conclusion, elderly patients with deep-vein thrombosis represent a particularly vulnerable population with numerous comorbid conditions. Diagnosis can present a challenge because typical deep-vein thrombosis symptoms may be absent. Fewer than 50% of elderly patients with deep-vein thrombosis had received any venous thromboembolism prophylaxis.