Abstract: Objective:To improve the CT diagnostic accuracy of primary mediastinal yolk sac tumor. Methods:The clinical manifestations and CT features of 13 cases with primary mediastinal yolk sac tumor were analyzed retrospectively. Results:All the 13 patients were young males, aged 18-33 years old, with an average age of 25 years old. All the tumors were located in the anterior mediastinum, including 7 cases in the right anterior mediastinum, 2 cases in the left anterior mediastinum, and 4 cases in the anterior middle mediastinum. Seven of the 13 patients were tested for serum alpha-fetoprotein (AFP), all of which were higher than normal. In 12 cases, the diameter was greater than 8cm, 9 cases showed uneven enhancement after enhancement, and 4 cases showed uniform enhancement. Twelve cases were closely related to the great vessels, among which 6 cases obviously surrounded the adjacent great vessels. Pleural effusion was found in 6 cases, pericardial effusion in 3 cases. There were enlarged mediastinal lymph nodes in 3 cases. Conclusion:Primary mediastinal yolk sac tumor is more likely to occur in young men, often located in the anterior mediastinum, with a large lesion volume and multiple cystic necrotic areas. CT can clearly show the relationship between the lesion and adjacent blood vessels, and combined with AFP detection can help improve its diagnostic accuracy.