In patients with deep vein thrombosis (DVT), the factors which predispose to concomitant symptomatic pulmonary embolism (PE) have remained uncertain. From a prospective cohort of 5,451 consecutive patients with ultrasound-confirmed DVT, we analyzed 4,211 patients with a known status for presence (n=639) or absence (n=3572) of symptomatic PE. Age and gender were similar in DVT plus PE (63.7+/-15.6 years; 49% men) and DVT patients (63.4+/-17.3 years; 46% men). Body mass index (BMI) was higher in patients with DVT plus PE (median 29.0, range 15.4-67.0 kg/m2) than in patients with DVT (median 26.8, range 9.7-64.4 kg/m2; p<0.001). Chronic lung disease (17% vs. 12%; p<0.001), a personal history of PE (11% vs. 6%; p<0.001), and a family history of DVT or PE (8% vs. 4%; p<0.001) were more frequent in DVT plus PE patients. Twenty-seven percent of DVT plus PE patients received prophylaxis prior to the thromboembolic event compared with 32% of DVT patients (p=0.002). Proximal DVT (OR 1.84, 95% CI 1.39-2.43), prior PE (OR 1.68, 95% CI 1.20-2.35), obesity (BMI >30 kg/m2) (OR 1.65, 95% CI 1.33-2.04), chronic lung disease (OR 1.51, 95% CI 1.13-2.01), as well as omission of prophylaxis (OR 1.30, 95% CI 1.04-1.64) emerged as independent predictors of concomitant symptomatic PE.