Purpose: This study was undertaken to determine the hypotheses that leaner individual with low body fat is a predisposing factor of nontuberculous mycobacterial (NTM) lung disease. Methods: Following a retrospective review of clinical data and radiographic findings of the chest between January 2005 and December 2011, 119 patients with NTM lung disease were enrolled in this study. We evaluated the extent of lung involvement on chest computed tomography (CT) based on the lobar distribution and subcutaneous fat mass (SFM) using cross-sectional CT scans at mid pole level of left kidney. An age- and sex-matched control group consisted of 51 with negative chest CT finding. We compared the SFM between the control and NTM lung disease, and evaluated relationship between SFM and disease severity according to the extent of NTM lung disease. Results: The median age of patients was 62 years (range, 23-95), and 70 patients (58.8%) were female. 33 were classified into the cavitary group (27.7%), and 86 into bronchiectatic group. The patients were significantly thinner (body mass index, 20.1 vs. 25.2; p＜0.0001) than control subjects. The NTM lung disease group had significantly lower SFM than the control group (39.4 vs. 58.7, p=0.001). There was no significant difference in SFM between localized (≤3 lobes) disease and extensive (＞3 lobes) disease (43.5 vs. 34.8, p=0.105). Conclusion: Patients with NTM lung disease had low body fat and slender morphotype with low BMI. Low body fat appears to be responsible for host susceptibility to NTM lung disease.