Mycobacterium abscessus is one of the species of rapidly growing mycobacteria that is widely distributed in nature. Using PCR-RFLP method, we have isolated 5 cases of M. abscessus from the soft tissue, sputum and blood, and further investigated each patient’s clinical courses and the results of the treatment. Three of the five patients had soft tissue infections, while the other two had pulmonary infections. Among the patients with soft tissue infections, two had a past history of steroid injection and the other had a trauma history. The clinical courses of these patients deteriorated quickly and they did not respond to the common anti-microbial antibiotics treatment. One of the two pulmonary infection patients, who had a past history of pulmonary tuberculosis and diabetes mellitus, had a more severe clinical course and difficulty on treatment than the patient who did not have a significant past history. M. abscessus can cause disseminated infection in immunocompromised patients and it most likely becomes resistant to antituberculous drug, therefore it is utmost necessary to perform rapid species identification and antibiotics susceptibility test. (Korean J Clin Microbiol 2004;7(1):84-89)