We report herein the case of a 68-year-old man in whom a partial anomalous pulmonary venous connection (PAPVC) was found during an operation for primary lung cancer. The preoperative clinical findings did not suggest a vascular shunt, and intraoperatively the anomalous vein was seen to drain only from the left upper lobe into the left innominate vein. The lower pulmonary vein connected normally, and there was no atrial septal defect nor any other anomalous condition. A left upper lobectomy with ligation of the anomalous connected vein was performed uneventfully. This type of PAPVC is extremely rare, and is especially noteworthy because there were no clinical signs.