Azygos vein varix is a very rare disease associated with a risk of rupture or thrombosis. Here, we report a case of azygos vein varix mimicking bronchogenic cysts. A 79‐year‐old female patient presented with abnormal shadows on a chest X‐ray during an annual check‐up. A plain chest computed tomography (CT) showed a well‐defined tumour, approximately 66 X 65 X 45 mm in size, behind the trachea. An enhanced CT scan was refused due to asthma complications. A high signal on T2W1 images from magnetic resonance imaging (MRI) indicated a cystic tumour. Diagnosed as a bronchogenic cyst, a cyst excision was scheduled. Upon observation with a thoracoscope, a dark purple‐red saccular tumour was observed continuing on to the azygos vein and was removed using linear staplers. The patient is alive and well 4 years after the operation. If a cystic tumour located in the right upper mediastinum is observed, the presence of azygos vein varix should be considered.