OBJECTIVE To present a case of unilateral vocal fold paralysis due to Mycobacterium kansasii induced pressure on the left recurrent laryngeal nerve, a specific aetiology not previously reported in the world literature. METHODS A 57-year-old Caucasian man presented with a short history of productive cough, fever, hoarseness and 14-kg weight loss. He was a smoker, had an abnormal chest X-ray and was human immunodeficiency virus negative. A sputum sample was positive on direct microscopy for acid fast bacilli. Initially, the patient was treated with Rifater (rifampicin, isoniazid and pyrazinamide) and ethambutol. Mycobacterium kansasii was isolated and proved sensitive to this antimycobacterial treatment. Nasoendoscopy revealed diminished movement of the left vocal fold, and a computed tomography scan showed enlarged mediastinal lymph nodes anterior to the aortic arch. After three months of antimycobacterial treatment, the vocal folds were fully mobile at repeat nasoendoscopy, and this coincided with gradual resolution of the patient's hoarseness and weight loss. CONCLUSIONS There are many causes of unilateral vocal fold paralysis. This case illustrates the importance of anatomical knowledge in reaching a diagnosis, and also presents the first reported case of Mycobacterium kansasii creating this clinical picture.