We encountered two cases of duplication of the inferior vena cava (IVC) in the Japanese cadavers of a 91-year-old man and a 71-year-old woman. Both of the anomalies were classified as Type BC and as Type I according to the systems of Chuang et al. (1974) and of Sarma (1966), respectively. In one case the right IVC was twice the diameter of the left IVC, and in the other it was five times as large. We discuss the clinical importance and the development of duplication of the IVC.