In a case control study, we assessed the prevalence of bacterial urinary tract infections (UTI) and renal scarring in 155 consecutive type 1 (n=102) and type 2 (n=53) diabetic individuals and 128 healthy controls. Subjects who received antibiotics during the past 6 months, pregnant women and those with overt renal failure were excluded. In all subjects, urine culture and 99m Technetium (Tc) dimercapto-succinic acid renal scan was performed. UTI was diagnosed if two consecutive urine cultures grew the same organism with at least 10(5) colony forming unit (cfu)/ml in asymptomatic and at least 10(4) cfu/ml in symptomatic subjects, respectively. Renal scan was considered abnormal if focal or multiple tracer uptake defects and/or break in cortical outline were observed. The prevalence of UTI in diabetes mellitus was higher, when compared to that in controls (9% vs. 0.78%, P=0.005). Escherichia coli was the most commonly grown organism (64.3%), followed by Staphyloccocus aureus (21.4%) and Klebsiella pneumoniae (14.3%). Prevalence of renal scarring was higher in patients with diabetes (28/155, 18.0%), when compared to that of controls (7/128, 5.4%, P=0.002). Fifty percent of patients with diabetes and UTI had renal scarring. The prevalence in diabetics with no UTI was also higher, when compared to controls (14.8 vs. 5.5%, P<0.01). The prevalence of UTI as well as renal scarring was significantly higher in females, when compared to male diabetics. No significant difference in vascular events, hypertension, proteinuria, renal function tests and HbA1 was observed in patients with and without renal scar. Thus, patients with diabetes mellitus have 10- and 3-folds increased risk of UTI and renal scarring, respectively. The results could help prioritize protocols for management of UTI among patients with diabetes mellitus.