The aim of the study was to assess whether diabetic patients with autonomic neuropathy suffer from arterial oxygen desaturation during sleep. Two groups of subjects were evaluated: group I consisted of 12 patients with cardiovascular autonomic neuropathy (five with insulin-dependent diabetes mellitus (IDDM) and seven with non-insulin-dependent diabetes mellitus (NIDDM)). Group II consisted of 8 healthy subjects. Age, percentage male and body mass index (BMI) were similar in both groups. Exclusion criteria were abnormalities in arterial gas measurements, chest X-ray, spirometry or the presence of cardiac arrhythmias, obesity, uremia, alcohol abuse and use of drugs other than insulin and oral hypoglicemic agents. The results of arterial oximetry when the subjects were awake showed no differences between the two groups. However, during sleep, diabetics with autonomic neuropathy had an increased number of desaturation episodes under 85% and those episodes were more prolonged. The results suggest that diabetics with autonomic neuropathy might have abnormal control of respiration that is apparent only during sleep.