The aim of the present study was to determine whether patients with bronchiectasis and nontuberculous mycobacteria (NTM) have a higher prevalence of Aspergillus-related lung disease. A series of 30 consecutive patients with bronchiectasis and NTM (cases) were compared with 61 patients with bronchiectasis and no evidence of NTM (controls). Aspergillus serology and computerised tomography of the thorax were used to identify Aspergillus-related lung diseases, including aspergilloma, allergic bronchopulmonary aspergillosis and chronic necrotising pulmonary aspergillosis. The rate of positive Aspergillus serology was higher in cases with NTM disease compared with controls (10 out of 30 versus six out of 61). The radiological features of Aspergillus-related lung disease were also more common among patients with NTM disease than controls (six out of 30 versus none out of 61). This association between NTM disease and Aspergillus-related lung disease remained significant after adjustment for confounding effects of age and lung function (adjusted odds ratio 5.1, 95% confidence interval 1.5-17.0). Patients with bronchiectasis and nontuberculous mycobacterial disease have a higher prevalence of coexisting Aspergillus-related lung disease than patients with bronchiectasis and without nontuberculous mycobacteria. Identification of Aspergillus-related lung disease is important as prognosis amongst undetected cases is invariably poor.