The azygos veins in thirty six cadavers (26 adult bodies, 10 human fetuses) were examined with special reference to the correlation with the midline of the vertebral column. The azygos veins were often observed to cross the middle of the ventral side of the vertebral column from right to left, and the occurrence of this crossing to the left is more frequent than that previously described--occurring in twenty two of the adult bodies. In three of the adult bodies, the vein ran upwards along the midline. In the remaining adult, the azygos vein ascended on the right side only of the vertebral column. In the fetuses, no azygos vein crossed the midline and the vein lay only on the right side or along the midline of the vertebral column. these results indicate the possibility of leftward displacement of the azygos vein during the aging process.