The present study aimed at accessing the natural history of untreated asymptomatic bacteriuria in diabetic patients observed for 14 years. Two groups of diabetic patients were examined. Group I comprised 53 patients with significant bacteriuria, without clinical symptoms of urinary tract infection. Group II consisted of 54 patients with sterile urine. All patients were clinically and bacteriologically examined every 3-6 months for 14 years. The results obtained in this study have proved that clinical symptoms of acute pyelonephritis occur with similar frequency in both groups (group I-6, group II-5 cases). No deterioration of kidney function was found. Arterial hypertension did not differ significantly in both groups at the beginning and end of the follow-up. The usefulness of antibacterial treatment of asymptomatic bacteriuria in diabetic patients is not adequately documented.