We herein report two cases of multidrug-resistant tuberculosis (MDR-TB) in patients with a history of pulmonary nontuberculous mycobacteriosis (PNTM). A 50-year-old man was diagnosed with MDR-TB five years after receiving treatment for pulmonary Mycobacterium kansasii infection. In the second patient, a 72-year-old woman, the diagnosis of PNTM was confirmed twice with two bronchial washings; she was diagnosed with MDR-TB 29 months after presenting with PNTM. It is highly possible that these two patients were already infected with tuberculosis (TB) at the time of PNTM diagnosis and acquired resistance to anti-TB drugs as a result of undergoing treatment for PNTM.