In Korea, the prevalence of nontuberculous mycobacterial (NTM) pulmonary disease has risen, observed primarily in immunocompetent patients with or without preexisting lung disease. The purpose of this study was to determine the frequency of various species of NTM isolates from respiratory specimens in a single institution over a 14-year period in Korea. All samples referred to our reference laboratory over a 14-year period in Korea were analyzed. From 1993 to 2000 our laboratory used conventional NTM identification methods, and from 2001 we adapted PCR-restriction fragment length polymorphism analysis(PRA). A total of 17,915 isolates were collected from 1993 to 2006. The most frequently isolated organisms were M. avium complex (n=11,705, 65%), M. abscessus (n=2,076, 11.59%), M. fortuitum complex (n=1,279, 7.14%). M. chelonae complex (n=1,134, 6.33%), M. kansasii (n=762, 4.25%), M. szulgai (n=139, 0.78%), M. celatum (n=87, 0.49%), M. scrofulaceum (n=18, 0.10%) and M. marium (n=11, 0.06%).