Thymoma is the most common primary tumor of the anterior mediastinum, accounting for 20% to 30% of all mediastinal tumors. The recurrence rate after total resection of the thymoma ranges from 8% to 18%. The authors describe a patient with recurrent malignant thymoma imaged with Tc-99m MIBI, Tc-99m tetrofosmin, and Tc-99m (V) DMSA. Early and delayed Tc-99m MIBI and Tc-99m tetrofosmin scintigraphy showed increased uptake in the mediastinal area, as did Tc-99m (V) DMSA scintigraphy. Coronal SPECT images obtained with Tc-99m MIBI, Tc-99m tetrofosmin, and Tc-99m (V) DMSA showed increased uptake in the mediastinal lesion seen on a computed tomograph of the chest. However, the normal blood-pool activity of the heart and great vessels imaged with Tc-99m (V) DMSA obscured the recurrent malignant thymoma. Although Tc-99m (V) DMSA is a useful tumor-seeking agent, Tc-99m MIBI and Tc-99m tetrofosmin SPECT are preferred to Tc-99m (V) DMSA to detect primary and recurrent malignant thymoma.