A 65-year-old man undergoing postoperative chemotherapy for rectal cancer was admitted to our department because disseminated granular shadows had been observed in both lung fields on chest computed tomography. Initially, sputum culture for acid-fast bacteria was negative. After about 8 weeks, the sputum culture became positive, as did TB-PCR testing. On the basis of these examinations, we diagnosed disseminated acinar pulmonary tuberculosis and began treating the patient with antituberculosis drugs (rifampicin, isoniazid, ethambutol, and pyrazinamide) 7 months after completion of his cancer chemotherapy. The shadows improved after treatment, about 5 years after the cancer chemotherapy ended; about 4 years after the end of tuberculosis therapy, neither disease has recurred. To our knowledge, this is the first case of disseminated acinar pulmonary tuberculosis developing during postoperative chemotherapy for rectal cancer. It is important to remember that the presence of cancer and also cancer therapy have the potential to trigger tuberculosis.