We investigated the expression of oncogenes p53, c-erbB-2, and bcl-2 and cell proliferative activity in 62 newly diagnosed superficial pTa papillary bladder tumors. Based on the 1998 World Health Organization/International Society of Urological Pathology (WHO/ISUP) and 1999 WHO classifications, 19 were urothelial neoplasias of low malignant potential (LMP) and 43 low-grade (grade 1) papillary carcinomas. All the patients underwent transurethral resection and were followed up to 97 months; 42 had recurrences. Initial biopsies were tested for p53, c-erbB-2, and bcl-2 proteins using DO7, CB11, and bcl-2 124 monoclonal antibodies. Cell proliferation was assessed by MIB-1 mAb and mitotic count. LMP had significantly lower MIB-1 (p = 0.002) and p53 immunopositivity (p = 0.03), mitotic count (p = 0.006), and recurrence rates (p = 0.04) than did grade 1 cases, whereas no difference was observed for c-erbB-2 and bcl-2 expression. The median disease-free survival for LMP was 76 months but only 15 months for grade 1 cases (p = 0.002). Although the cohort is small, the results indicate that the distinction between LMP and low-grade (grade 1) papillary urothelial neoplasias, as proposed by the 1998 WHO/ISUP and 1999 WHO classifications, reflects different biologic activity and clinical behavior; however, a long-term follow-up is advisable also for patients with LMP.