One hundred fourteen cases of bladder cancers treated during a 3-year period by cystectomy were uniformly reclassified, graded, and pathologically staged. One hundred thirty-one cases treated during the same period by transurethral or segmental resection were similarly reclassified and checked for muscle invasion. Sixty-one percent of the cystectomy cases were nonpapillary and 69% of the conservatively treated cases were papillary transitional cell carcinomas. In the pathologically staged cystectomy group, all poorly differentiated (grade III and IV) carcinomas were invasive. Nonpapillary tumors were more aggressive and 79% of the high grade tumors in these categories extended into the outer portions of the muscularis or into perivesical tissues. Muscle invasion could also be demonstrated in 74% of the 23 high-grade nonpapillary carcinomas in the conservatively treated cases. Lymph node and pelvic wall metastases were found in 17% of the cystectomies and were present only in tumor grades III and IV and a pathologic stage of P-3B or higher. None of the well differentiated (grade I) papillary carcinomas were invasive and invasion was superficial in most moderately differentiated (grade II) papillary tumors. The findings confirm that pathologic classification and grading of bladder carcinomas correlate closely with the stage of the disease.