Diaphragmatic recurrence of a thymoma is rare. We report the case of a 70-year-old woman who underwent transternal thymectomy and adjuvant radiation therapy, and who was admitted four years later with recurrence of the thymoma in the left hemidiaphragm with infiltration of the inferior ipsilateral pulmonary lobe. The thymoma was excised along with the left hemidiaphragm, chest wall and three ribs and an atypical segmentectomy of the left lower lobe was performed. The hemidiaphragm was reconstructed and the chest wall was repaired with synthetic mesh. Surgery was complemented with radiotherapy.