Factor V Leiden (FVL) is the most common genetic polymorphism known to predispose to episodes of venous thromboembolism (VTE) in western countries; heterozygosity for FVL occurs in 3–8%, and the rate of homozygosity is around 1/5,000 in the general population in Italy1. As previously reported, we observed a very high prevalence of FVL carriers in patients with deep venous thrombosis in Chioggia. Among 292 consecutive patients attending our Laboratory for investigation of thrombophilic risk factors after an episode of venous thrombosis we observed 168 (57.5%) normal subjects and 124 (42.5%) FVL carriers: 13 (4.5%) of whom were homozygous for the polymorphism and 111 (38.0%) heterozygous2,3. The high prevalence of FVL carriers among patients with venous thrombosis should be due to case selection but may also reflect a high diffusion of this particular mutation in Chioggia. The aim of this study was to establish the correct prevalence of FVL carriers in our area by evaluating patients, their blood relatives and the general population.