In 11 patients with pulmonary disease due to Mycobacterium xenopi, definite aspergilloma subsequently developed in five and probable aspergilloma in a further three. Those patients with evidence of Aspergillus infection formed a much higher proportion (73%) than in previous reports of patients with mycobacterial disease. Patients with both Mycobacterium xenopi infection and aspergilloma appear to have a poor prognosis.