Pulmonary blastoma is a rare malignant tumor, histologically resembling the fetal lung. Since its first description in 1945, only about 200 cases have been reported worldwide. This tumor predominantly affects children, but has also been reported in adults with a peak incidence in the fourth decade of life. Pulmonary blastoma has a variable clinical course that cannot be determined by its histological appearance. We report a 51-year-old patient with a large biphasic pulmonary blastoma who was treated with surgical excision. The patient remains disease-free eleven months postoperatively. As relapse rates are high in patients with large biphasic (type 2) tumors, the patient is being monitored closely. Although a rare occurrence after the age of 20, pulmonary blastoma should remain in the differential diagnosis of a lung mass in an adult.