A previously undiagnosed case of myotonic dystrophy presenting with apnoea of 2.5 h duration following thiopentone is described. A review of the anaesthetic outcome from 49 operations in 17 patients with myotonic dystrophy in the Aberdeen area is presented. The type of operation and intra- and postoperative problems are analysed. The results reveal a 52% complication rate in previously diagnosed cases and a 35% complication rate in undiagnosed cases. In the series, 29% of the anaesthetics were administered to symptomatic patients before formal diagnosis. To avoid potential hazards it behoves the anaesthetist to remain alert to the possibility of the undiagnosed disease. The symptomatology and associated findings of the 17 patients at initial diagnosis are presented. The literature has been reviewed and anaesthetic implications noted.