Mycobacterium chelonae (M. chelonae) is rarely responsible for respiratory infection. This report concerns the case of an 81-year-old man with previously asymptomatic bronchiectasis, colonised by M. chelonae for 3 years. He was hospitalised for acute dyspnoea and fever due to a right hydro-pneumothorax with cavitated alveolar opacities of the right lung. Pleural fluid and bronchial aspiration were positive for M. chelonae and no other microorganisms were detected. The effusion was drained and the patient treated with clarythromycin and amikacin. The radiological abnormalities improved but the patient's general condition remained poor. Treatment was continued for 11 months. Because of the absence of any other bacteria, clinical deterioration following broad-spectrum antibiotics and stabilisation of the lesions after anti-mycobacterial treatment, our diagnosis was severe M. chelonae pleuro-pneumonia in an immunocompetent patient.