Mycobacterium kansasii is the second most common cause of nontuberculous mycobacterial pulmonary disease in Western countries and Japan. The clinical and radiological features of pulmonary disease caused by M. kansasii usually resemble those of pulmonary tuberculosis including cavitary infiltrates with an upper lobe predilection. It is also now apparent that patients with M. kansasii pulmonary disease can present with noncavitary nodular bronchiectatic infiltrates similar to lung diseases of M.avium complex. With rifampin-containing regimens, treatment success rates are almost 100%. Timely diagnosis before the development of extensive disease and effective overall treatment strategies are very important to ensure that patients receive the appropriate medications for a sufficiently long period of time. To our knowledge, there has been no Korean case report of M. kansasii pulmonary disease in the immunocompetent patient until now. We report three cases of M. kansasii pulmonary disease in immunocompetent adult patients.