Asymptomatic erythrocyturia is an early symptom of urinary tracts and kidney diseases, including bladder carcinoma. The aim of the research was to compare the diagnostic validity of the cytological urine analysis and the DNA flow cytometry in detecting cancer cells in urine and bladder washings, taken from patients with asymptomatic erythrocyturia, as an early symptom of the bladder carcinoma in situ. The research was conducted on a group of 48 patients (32 male, 16 female, aged 28-55) with asymptomatic erythrocyturia, caused, in 16 cases, by bladder carcinoma in situ, in 18 cases, by bladder carcinoma in situ with urinary tracts infection, and in 14 cases, by the infection alone. Flow cytomery showed a higher sensitivity and a higher negative prediction value in detecting cancer cells in bladder washings. Flow cytometry analysis of DNA and phase S is used for detecting early disturbances in the cell cycle which result in aneuploidia, which is impossible to detect in cytological analysis. However peculiarity and positive prediction value were the same (100%) in both methods. On the basis of the research it has been proved that asymptomatic erythrocyturia classifies patients for further, in-depth diagnostic examination for the presence of bladder carcinoma in situ. Furthermore, morning urine and bladder washings analysis, which are non-intrusive tests, are an outstanding diagnostic material for screening for this disease. Detecting aneuploidia with flow cytometry can be an early-detection screening test for bladder carcinoma, while the cytological tests should still be used for confirming the diagnosis.