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The venous system variations are generally explained on the basis of their embryological development. Tributaries of the azygos venous system varies greatly. Variations of azygos venous system and especially of the hemiazygos veins are not clearly described in the literature. In this case, the azygos vein instead of lying on the right side of the vertebral column was in the midline of posterior mediastinum. The left azygos venous line was ill defined and lower left posterior intercostal veins were opening independently into the azygos vein. The left superior intercostal vein was opening into the azygos vein. The accessory hemiazygos vein was ill defined. The origin and termination of the azygos venous system was found normal. These variations are discussed in view of its embryological development. Clinically these variations should be kept in mind while doing mediastinal surgery of large vessels.