Women with diabetes mellitus (DM) have asymptomatic bacteriuria (ASB) and urinary tract infections (UTIs) more frequently than women without DM. For type 1 diabetes mellitus, risk factors for asymptomatic bacteriuria include a longer duration of diabetes, peripheral neuropathy and macroalbuminuria. For type 2 diabetes, the risk factors are higher age, macroalbuminuria and a recent symptomatic UTI. Poorly-controlled diabetes and residual urine after urination are no risk factors. The most important risk factor for a UTI in type 1 diabetes patients is sexual intercourse. In type 2 diabetes patients the major risk factor is the presence of asymptomatic bacteriuria. This higher prevalence does not appear to be based on a difference in virulence of the causative microorganism. Differences in host response may explain this higher prevalence: E. coli with type 1 fimbriae adhere better to uroepithelial cells in women with DM than to those in women without DM; women with DM and ASB have lower urinary cytokine concentrations and leukocyte counts compared to women without DM and ASB; in vitro studies show that E. coli grow better when glucose is present in urine. There is no consensus on whether ASB should be treated in these patients. There are indications that UTIs in diabetes patients should be treated as complicated UTIs.