Flow-cytometric (FCM) DNA analysis was performed in 534 samples from 140 bladder tumor cases and was compared with histopathological findings. Frequency of DNA aneuploidy was closely correlated with tumor grade. Namely the incidences of DNA aneuploidy were 20% in grade 0 (papilloma), 25.6% in grade 1, 57.7% in grade 2 and 95.7% in grade 3. Invasive tumors showed a significantly higher incidence of DNA aneuploidy than superficial papillary tumors. Frequency of DNA aneuploidy of CIS was between them. Nonpapillary tumors showed a significantly higher incidence of DNA aneuploidy than papillary tumors. Tumors with vessel invasion did show a similarly higher incidence than those without. Approximately 10% of histologically normal mucosa taken from the bladder tumor patients showed DNA aneuploidy. The present study could support possibilities that FCM findings were highly correlated with tumor malignant potentials and were also able to predict precancerous lesions on histologically normal mucosa.