Objective: To evaluate the prevalence of Mycobaterium Tuberculosis complex and Nontuberculous mycobacterial (NTM) pul-monary infection after using specimen grown in liquid medium. Methods: Patients with positive acid-fast bacilli (AFB) culture from november 2011 to september 2012 at Chonnam National University Hospital were retrospectively reviewed. To identify NTM lung disease, we then reviewed the clinical and radiologic characteristics of the patients from whom NTM was isolated. Results: During the study period, Of a total of 465 patents with 947 positive AFB cultures, 451 NTM isolates were recovered from 258 patients. Patients with NTM isolates were 140 male and mean age were 67 (range 19-93). NTM isolates were Mycobacterium avium complex (n=104, 40.3%) and Mycobacterium abcessus (n=18, 7%). NTM species identification was not performed for 123 NTM isolates. Of these 258 patients, 69 patients (26.7%) were determined to have definite NTM lung disease, 39 patients (15.1%) had respiratory symptoms and chest images without NTM species idendification. Of 69 patients with NTM lung disease were Mycobacterium avium complex (n=56, 81.2%) and Mycobacterium abcessus (n=11, 15.9%). In 69 patients with NTM lung disease, 16 patients (23.2%) manifested the cavitary form, 27 patients (39.1%) exhibited the bronchiectatic form and 26 patients (37.7%) revealed the nodular or consolidative form. Conclusions: About one half of positive AFB culture were NTM isolates. And then one half of patients whom was NTM isolated had clinically significant NTM lung infections.