In recent decades, an increasing incidence of pulmonary infections with non-tuberculous mycobacteria has been reported, primarily affecting patients with structural lung diseases and/or immunosuppression. In Denmark, approximately 100 new cases of infection with non-tuberculous mycobacteria occur yearly, most commonly with Mycobac-terium avium complex. Diagnosis is based on clinical, radiological and microbiological criteria. Treatment is difficult, and outcomes are often poor. Antibiotic treatment should be performed by specialists with reference to international guidelines.