Introduction: Our objective was to evaluate the feasibility and value of microstaging in pT1 transitional cell carcinoma (TCC) of the bladder in a well-defined group of patients treated with transurethral resection (TUR) only. Materials and Methods: The clinical records of 152 patients who underwent TUR for the treatment of primary superficial TCC of the bladder between 1983 and 1997 were reviewed. Patients with primary carcinoma in situ and who received adjuvant intravesical treatments were excluded from study. We subclassified the pT1 tumors into two groups according to muscularis mucosae (MM) invasion (pT1 and pT1b). The recurrence and progression rate of cancers was analyzed according to the stage, grade, multiplicity and tumor size. Mean follow-up was 68 months. Estimation of the cumulative distribution of the disease-free interval in separate groups was calculated according to the Kaplan-Meier method. Multivariate analysis of the data was performed by using Cox regression method. A value of p < 0.05 was taken to be statistically significant with odds ratios. Results: Of the 152 patients, tumor stage was pTa in 62 (40.8%) patients and pT1 in 90 (59.2%) patients. Among those pT1 tumors, MM was identified in 50 (55.5%) of cases (pT1a = 34, pT1b = 16). In the remaining 40 (44.5%) patients, MM could not be assessed. Kaplan-Meier analysis revealed that recurrence and progression were statistically significant for stage, multiplicity and grade of tumor. However, multivariate analysis revealed that stage was the only prognostic factor for recurrence and progression (p 0.0001). Conclusion: The present study underscores the fact that pT1b tumors have a distinct natural history. If initial conservative treatment is selected, the patients must be followed very cautiously. Copyright (C) 2002 S. Karger AG, Basel.