Cardiopulmonary bypass has been reported to have many effects on the immune system. The aim of this study was to investigate the efficiency and usefulness of off-pump coronary artery bypass (OPCAB) surgery on patients who had coronary artery disease besides malign neoplasia. We applied OPCAB operations to 217 patients between March 2001 and April 2004, ten of whom had malign neoplasia. These patients were diagnosed to have coronary artery disease on their routine examination for their oncologic operation. The malignancies were stomach cancer (2 patients), colon-rectum carcinoma (3 patients), breast carcinoma (2 patients), surrenal carcinoma (1 patient), larynx carcinoma (1 patient), and meningioma (1 patient). The patients were operated on for their neoplasia by the related clinics at a mean of 42 days after the OPCAB surgery. The patients were discharged with surgical success and without any cardiac complications. Coronary artery bypass surgery before a noncardiac major operation may effectively decrease the long-term mortality due to myocardial ischemia. Severe coronary artery disease should be surgically treated in those patients who are scheduled to undergo an operation for malign neoplasia. Extracorporeal circulation impairs the immune system and negatively affects the defense of host against malignancy. Therefore, patients with severe coronary artery disease who are candidates for oncologic operation should be treated with OPCAB.