High-grade T1 bladder cancer has a poor prognosis due to a higher incidence of recurrence and progression than other nonmuscle invasive bladder cancer; thus patients with high-grade T1 have to be carefully monitored and managed. If patients are diagnosed with high-grade T1 at initial transurethral resection (TUR), a second TUR is strongly recommended regardless of whether muscle layer is present in the specimen because of the possibility of understating due to incomplete resection. Since high-grade T1 disease shows diverse clinical courses, individual approaches are recommended for treatment. In cases with low risk of progression, cystectomy could represent overtreatment and deteriorate quality of life irreversibly, while, in those with high risk, bacillus Calmette– Guérin (BCG) therapy may worsen survival by delaying definitive therapy. Therefore, a strategy for predicting prognosis based on the risk of progression is needed for managing high-grade T1 disease. Molecular risk classifiers predicting the risk of progression and response to BCG may help identify the optimal management of high-grade T1 disease for each individual.