Purpose: To compare diffusion-weighted magnetic resonance imaging (DW-MRI) with cystoscopy in the diagnosis and follow-up of patients with bladder tumor and to investigate any histopathological correlation. Materials and Methods: Totally 59 patients, between 31-85 years (mean age 60 +/- 13) referred to our clinic due to a hematuria complaint were enrolled and evaluated by upper urinary system pathology and then DW-MRI (average 7 days) and cystoscopy. Apparent diffusion coefficients (ADCs) of images were calculated. Results: While a mass in bladder was determined with cystoscopy in 43 out of 59 patients, the mass was not deternined in 16 of the patients(n=34 malign, n=9 benign). While a mass was determined in 40 out of 59 patients with DW-MRI, the mass was not determined in 19 of the patients(n=40 malign, n=19 benign). Regarding ADC values, mean ADC values of 34 patients who were diagnosed with a bladder tumor (1.05 +/- 0.22 x 10(-3)mm(2)/s), were significantly lower than the mean ADC values obtained from the normal bladder wall (1.830 +/- 0.18 x 10(-3)mm(2)/s) whereas a statistically significant difference was found (p<0.001). ADC values in 9 patients with a benign lesion (1,73 +/- 0.12 x 10(-3)mm(2)/s), were not found statistically different from the mean ADC values obtained from the normal bladder wall (1.78 +/- 0.2x10(-3)mm(2)/s) (p>0.05). A significant difference was determined between ADC values of benign lesions and the ADC values of malign lesions (p<0.001). Conclusions: According to cystoscopy, values of DW-MRI's related with sensitivity, specificity and accuracy were found, respectively 90%, 93% and 91%. As the DW-MRI is a non-invasive and a rapid technique, and does not contain ionized radiation and because it is accepted as an important marker of tumor cellularity, it may be used as an alternative in future diagnosis and follow-up of bladder tumors.