We report the case of a 51-year-old man who presented with breathlessness on exertion and orthopnoea in association with Type 2 diabetes mellitus. Investigation showed bilateral diaphragmatic paralysis due to phrenic neuropathy. There was no evidence of neuropathy or microvascular disease elsewhere. Phrenic neuropathy may be an important, albeit rare, complication of diabetes and diaphragmatic function should be considered in any patient with unexplained breathlessness and orthopnoea.