Most T1 bladder cancers are high grade and have the potential to progress to muscle invasion and extravesical dissemination. Many studies reported that ∼50% of patients displayed residual tumors when a second transurethral resection was performed 2–6 weeks after the initial resection for patients who were diagnosed with T1 bladder cancer. Furthermore, muscle-invasive disease was detected by the second transurethral resection in 10–25% of those patients. Therefore, a second transurethral resection is strongly recommended for patients newly diagnosed with high-grade T1 bladder cancer in various guidelines. T1 bladder cancers are heterogeneous in terms of progression and prognosis after the second transurethral resection. Optimal management and treatment should be considered for patients with T1 bladder cancer based on the pathological findings for the second transurethral resection specimen. If the second transurethral resection reveals residual tumors, aggressive treatments based on the pathological findings should be performed. Conversely, overtreatment with respect to the tumor status should be avoided. Since the evidence of pathological diagnosis at the second transurethral resection is insufficient and many retrospective studies were carried out before the second transurethral resection era, prospective randomized studies should be conducted.