- The progression of bladder cancer to invasive disease is highly dependent on its ability to penetrate basement membrane of urothelium. Studies on diabetic nephropathy have shown a reduction in proteoglycan content of the glomerular basement membrane. Based on the well-known fact that proteoglycans are one of the main components of basement membrane and extracellular matrix we assessed the relationship between diabetes mellitus, bladder cancer incidence and its behavior. These studies include 252 patients with microscopically confirmed transitional cell carcinoma of bladder, and 549 patients with other urological disorders who served as controls. The prevalence of diabetes mellitus in each group was assessed. The group of patients suffering from transitional cell carcinoma was divided according to etiological risk factors such as cigarette smoking, diabetes and patients that were non-smokers and did not suffer from diabetes mellitus. We assessed the features of bladder cancer behavior in each group. Logistic regression model estimation for statistical analysis was used, with transitional cell carcinoma as a dependent binary variable and age, sexes smoking and diabetes as independent variables. Statistical significance was considered at two levels: p <-0.001 and p <-0.05. Odds ratio (OR) adjusted to age, sex, cigarette smoking, diabetes mellitus and 95% Confidence Interval (CI) were calculated for TCC. In the TCC group 22.2% of the patients suffered from diabetes mellitus. In the control group 10.38% suffered from diabetes mellitus. Logistic regression analysis, OR and 95% CI showed a statistically significant relationship between diabetes and TCC. These data are comparable only with smoking (OR -2.3; 95% CI -1.6 –3.5 and OR-1.58; 95% CI -1.08 –2.4 correspondingly). Based on these data we suggest that diabetes mellitus may be considered an etiological risk factor for bladder cancer development.