SUMMARY:The aim of the present study was to determine the most common origin of the azygos vein. Thirty cadavers male and female, white and non-white adult individuals of different ages fixed in 10% formaldehyde and dissected. All cadavers had an undisclosed clinical death and were donated to the Universidade Estadual de Ciências da Saúde de Alagoa s, Brazil. Eleven different formations were found. The right subcostal vein was was only observed in 13 cases (43.33%); the azygos vein was formed by the confluence of the right subcostal and right ascending lumbar vein in three cases (10%); by the right subcostal vein with a contribution from the inferior vena cava (IVC) in three cases (10%); by the right subcostal with contribution from IVC and right ascending lumbar vein in three cases (10%); by the right and left subcostal veins in two cases (6.66%); by the right and left subcostal veins and contribution from the IVC in one case (3.33%); by the right and left subcostal veins and left accessory renal vein in one case (3.33%); by the left renal vein in one case (3.33%); by the right subcostal and left gonadal veins with contribution from the IVC in one case (3.33%); by the right subcostal and left renal veins in one case (3.33%); and composed by the continuation of the 11th posterior intercostal vein in one case (3.33%). Based on the results, the right subcostal vein was the only structure with a significant presence in the formation of the azygos vein.