BCG is an effective treatment for high-risk non-muscle invasive bladder tumors, with response rates of around 70%. However, progression during BCG treatment can occur in 9.5%-21% of cases, resulting in a worse patient prognosis. If there is no response to BCG or BCG failure occurs, the European Association of Urology (EAU) guidelines have defined different types of BCG failure. Unresponsive tumors will require cystectomy, clinical trial, or other options different from BCG. They are divided into refractories, early relapsing, and late relapsing, with different risks of progression and prognosis. Low-grade recurrences during or after BCG are not considered BCG failure and can be treated with appropriate BCG doses.