Chronic pulmonary aspergillosis (CPA) is associated with mortality in patients with Mycobacterium avium complex lung disease (MAC-LD). An Aspergillus-positive respiratory specimen often reflects colonization, and thus the clinical significance of Aspergillus isolation in MAC-LD patients is not well understood. The objective of this study was to investigate the clinical characteristics and outcomes of MAC-LD patients in whom Aspergillus was isolated from respiratory specimens. We performed a retrospective review of the medical records of 329 MAC-LD patients. We compared the characteristics and mortality rates between patients with Aspergillus isolation and those without. All Aspergillus species detected from respiratory specimens within the follow-up period were reviewed. Aspergillus was detected in 40 (12.2%) of the 329 patients. There were no significant differences in the clinical characteristics and mortality rates between patients with and without Aspergillus isolation. Among the 40 patients with Aspergillus isolation, 9 (22.5%) developed CPA. CPA was most often caused by A. fumigatus. In the 40 Aspergillus-positive patients, patients with A. fumigatus isolation had a significantly higher mortality rate than those without (P < 0.001). The multivariate Cox proportional hazards model showed older age (P = 0.050), presence of respiratory comorbidities (P = 0.008), hypoalbuminemia (P < 0.001), and isolation of A. fumigatus (P = 0.005) to be prognostic factors for mortality in MAC-LD patients. There was no significant difference in the mortality rates between patients with Aspergillus isolation and those without. However, isolation of A. fumigatus may be associated with poor prognosis in MAC-LD patients.