We report a 70-year-old woman diagnosed with unicentric Castleman's disease with a contrast well-enhanced retroperitoneal tumor of 25 mm in diameter that located between the aorta and inferior vena cava. The imaging finding did not suggest any specific features, and no other lesion was detected. Laboratory examinations indicating malignant lymphoma such as soluble interleukin-2 were all negative. We resected the retroperitoneal tumor laparoscopically, and histopathological examination revealed hyaline vascular type Castleman's disease. Although complete resection of hyaline vascular type unicentric Castleman's disease results in a good prognosis, a late relapse has been reported and long-term follow-up is warranted.