A multiregional cross-sectional study of clinical diabetic polyneuropathy (DPN) was carried out among Spanish diabetes patients using a standard system for scoring symptoms and signs of polyneuropathy. The main patient sample comprised 2644 patients (54.7% women) aged 15-74 years (mean 57.2 +/- 0.3 years), 86.9% of whom had Type II (non-insulin-dependent) diabetes mellitus and 29.4% were attending hospital clinics. Mean duration of diabetes since diagnosis was 10.2 +/- 0.2 years. The prevalence of DPN was 22.7% (95% confidence interval 21.2-24.3%) in the whole sample, 12.9% (9.4-16.5%) among patients with Type I (insulin-dependent) diabetes mellitus and 24.1% (22.4-25.9%) among patients with Type II diabetes; there was no significant difference in prevalence between men and women. Prevalence increased with age (from < 5% in the 15- to 19-year-old age group to 29.5% in the 70- to 74-year-old group) and with duration of diabetes since diagnosis (from 14.2% among those with duration < 5 years to 44.2% among those with duration > 30 years). In a supplementary sample of 161 diabetic patients aged 75 to 79 years (excluded from the main sample to prevent confusion between diabetes-induced and ageing-induced neuropathies), prevalence was 37.8%. Ninety-three patients (3.3%) had or had had foot ulcers and 21 of these 93 (0.7%) had undergone amputation; 90.8% of ulcerated patients had Type II diabetes, and 54% had DPN (in most cases with loss of perception of vibration), as against a prevalence of DPN of 19.9% among patients without ulcers. We conclude that nearly a quarter of Spanish diabetic patients have DPN; that over 90% of DPN patients have Type II diabetes; that the prevalence of DPN increases with age and with the duration of the disease, and that the risk of foot ulcers among DPN patients is about three times the risk among diabetic patients without DPN. We accordingly emphasize the responsibility of primary care physicians to try to prevent diabetic foot lesions by early diagnosis of DPN.