The allocation of some symptoms of acute hypoglycaemia to autonomic and neuroglycopenic groups has proved problematical, with possible misinterpretation of studies which depend upon the use of diverse symptom questionnaires. Two hundred and ninety-five randomly selected insulin-treated diabetic patients were asked to report the symptoms which they usually experienced and believed to be caused by hypoglycaemia. Sweating, trembling, inability to concentrate, weakness, hunger and blurred vision were the most frequently reported symptoms. To classify symptoms of hypoglycaemia objectively, Factor Analysis was used to identify related symptoms which grouped together. This resulted in five groups or clusters of symptoms, four of which could be denominated as groups with a presumed common aetiology, and were labelled: 'neuroglycopenic', 'general malaise', 'autonomic', 'motor dysfunction', and 'sensory dysfunction'. The groups of symptoms derived by Factor Analysis were assessed in relation to partial or absent symptomatic awareness of hypoglycaemia based on historical evidence from the 295 insulin-treated diabetic patients. Neuroglycopenic symptoms were reported more commonly by the patients who had reported partial awareness of hypoglycaemia (number of symptoms 2.6 +/- 1.8 (mean +/- SD] than by the patients who had reported normal hypoglycaemia awareness (1.4 +/- 1.5 symptoms) (p less than 0.05). By contrast autonomic symptoms were reported less frequently by the patients who had reported absent hypoglycaemia awareness (1.3 +/- 1.4 symptoms) than by those with normal awareness (2.2 +/- 1.4 symptoms) (p less than 0.05), which was similar to the number of autonomic symptoms reported by the patients who had partial hypoglycaemia awareness (2.1 +/- 1.3 symptoms).