Although heterotopia of pancreatic tissue is a developmental anomaly found in approximately 2% of all autopsies, pancreatic tissue within the thorax and mediastinum is uncommon. In most of these instances, the pancreatic tissue is a component of gastroenteric duplication cysts, intralobar pulmonary sequestrations or teratomas. We describe an anterior mediastinal cyst consisting entirely of pancreatic tissue. A previously healthy 27-year-old woman was admitted due to chest pain during deep inspiration. The computed tomographic scan of the thorax showed a large cyst occupying the right anterior mediastinum. The excised multilocular cystic lesion measured 12 cm in maximum diameter and contained a brown, turbid fluid. The wall was fibrotic and showed a haphazard mixture of ducts and exocrine acini without islets. The histogenesis of this lesion is unclear.