Hearing thresholds were studied in 53 patients with insulin-dependent diabetes mellitus (IDDM) and 42 randomly selected non-diabetic control subjects, aged between 20 and 40 years. The hearing level tended to be worse in diabetic patients than in control subjects, but the differences were statistically significant only at frequencies of 6,000 and 8,000 Hz. Microvascular complications (retinopathy and nephropathy), and the duration of diabetes were associated with the elevated hearing thresholds. In contrast, poor metabolic control (high fasting blood glucose and glycated haemoglobin A1c) was not associated with increased hearing thresholds. The changes caused by diabetic neuropathy appeared simultaneously with microvascular complications and a long duration of the diabetes, and thus a causative role of diabetic neuropathy in the pathogenesis of elevated hearing thresholds remained unsolved. It was concluded that elevated sensorineural hearing thresholds at the frequencies of 6,000 and 8,000 Hz in patients with IDDM are probably caused by the long duration of diabetes and the microvascular complications associated with it.