CASE PRESENTATION: A 65-year-old non-smoker male patient with a history of bronchial asthma and suspected hypersensitivity pneumonitis due to pigeon exposure is presented, with medical data available spanning fifteen years of routine examinations. The patient presented anew in 2014 with recurrent respiratory tract infections, ineffective sputum clearance and uncontrolled asthma. The spirometry results had markedly worsened compared to earlier. The pigeon precipitin test results were positive but HRCT findings were not suggestive of an extrinsic allergic alveolitis. However, HRCT imaging revealed tracheobronchomegaly, with tracheal and bronchial diverticula and bronchiectasis compatible with Mounier-Kuhn Syndrome (Figure 1). In retrospect, HRCT scans from another hospital eight years earlier also demonstrated signs of tracheobronchomegaly, diverticula and bronchiectasis. Bronchoscopy was performed supporting the diagnosis of Mounier-Kuhn Syndrome (Figure 2). The patient was treated with appropriate antibiotics in addition to other supportive measures. The patient’s symptoms and pulmonary function improved under the given treatment.