A prospective study was done to evaluate treatment of patients with muscle-infiltrating bladder cancer by transurethral resection exclusively. Inclusion criteria for this study were histological confirmation of muscular bladder infiltration, endoscopic radical transurethral resection, disappearance of hardened areas after transurethral resection, and negative biopsies of the depth and periphery of the tumor bed. The study began in April 1981. The average followup in series 1 (April 1981 to December 1986, 59 patients) was 55.4 months. Actually, of the patients 31 (52.5%) are without evidence of recurrence and 28 (47.5%) have recurrent disease. Of the latter patients 11 (18.6%) had invasive bladder recurrence, including 7 (11.9%) who had recurrence at 3 months, which indicated clinical understaging. Three patients (5%) had metastases without bladder tumor. The remaining 14 patients (23.7%) had superficial bladder recurrence. The overall survival rate was 83% (49 of 59 patients) and 43 patients (72.8%) still retain the bladder. The present data are confirmed by the results of series 2 (December 1986 to August 1989). Therefore, the data would justify conservative management in a selected group of patients with muscle-infiltrating bladder cancer.