Ventilatory failure may result from dysfunction of any part of the respiratory pathway. Muscle weakness preexisting or acquired should be considered in all patients. Case Report: A 52-year-old smoker presented in extremis with type II respiratory failure. She was treated with bronchodilators, steroids and antibiotics. Weaning ventilatory support was difficult and so a tracheostomy was performed.. Two weeks later, she was transferred to a respiratory ward where she was decannulated before discharge home. After discharge, her breathlessness and weakness progressed until she was readmitted in extremis 1 week later. On readmission, she deteriorated despite treatment for COPD. Mandatory ventilation was initiated after recannulation of the tracheostomy. The patient gradually improved over the next few days and was transferred to a respiratory ward where she was weaned onto nocturnal NIV and the tracheostomy was decannulated. Flow volume loops excluded air flow obstruction but spirometry confirmed severe inspiratory muscle weakness. The patient reported progressive weakness over several years. On examination all muscle groups were weak and deep tendon reflexes were absent but there was no fatigability or fasciculation. Sensation was intact. The diagnosis of acid maltase deficiency (AMD) was confirmed by analysis of peripheral blood lymphocytes, muscle biopsy and enzyme assay.