Objectives: The isolation of Mycobacterium szulgai from respiratory specimens were traditionally considered to be highly indicative of disease. However, the high clinical relevance is not consistent through the literature. The aim of this study is to determine the clinical significance of M. szulgai isolates from respiratory specimens and to identify the clinical features and outcomes of M. szulgai lung disease. Methods: We reviewed the medical records for 30 patients with M. szulgai isolates between 2001 and 2010 at the Samsung Medical Center. Results: Of the 30 patients, 13 (43%) met the American Thoracic Society diagnostic criteria and were thus likely to have true M. szulgai lung disease. Approximately 57% (17/30) of M. szulgai isolates were recovered only once from patients with other pulmonary diseases, such as pulmonary tuberculosis, and bacterial pneumonia. The 13 patients with M. szulgai lung disease included 12 men (92%), with a median age of 63 years. Seven (54%) were current smokers and 7 (54%) had a history of previous tuberculosis treatment. Eight (62%) patients had the fibrocavitary form of M. szulgai lung disease. Nine (69%) patients received antimycobacterial treatment for a median duration of 8 months. Negative culture-conversion was documented in all patients. There was no recurrence or disease-related mortality. Conclusions: Because the isolated M. szulgai from respiratory specimens could be regarded as pathogenic in less than 50% cases, it is important to evaluate patients` risk factors and adhere to the recommended diagnostic criteria.