Oral dantrolene is used widely for the treatment of spasticity in patients with spinal cord injury. A 60-year-old patient in the rehabilitation phase following cervical spine injury presented with generalised weakness and deteriorating respiratory function, requiring intensive care admission, tracheal intubation and ventilation. He had bilateral basal lung collapse and a raised diaphragm and was on high-dose oral dantrolene. The cessation of dantrolene resulted in a dramatic recovery of respiratory function within two days. High-dose oral dantrolene can cause severe respiratory insufficiency and may present difficulties in the differential diagnosis of respiratory failure in patients with high cervical spinal cord injuries.