Background Adjuvant Bacillus Calmette-Guerin (BCG) intravesical instillation is the recommended standard treatment in patients with high-risk non-muscle-invasive bladder cancer (NMIBC). However, a significant proportion of patients fail treatment, and radical cystectomy (RC) is the subsequent gold standard. On the other hand, there is an unmet need for conservative alternatives for patients who are unfit or unwilling to undergo surgery. This study aimed to identify conservative treatment options in NMIBC patients after BCG failure. Material and Methods We performed a systematic search in the databases Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE, including all randomised controlled trials (RCTs), quasi-RCTs and singlearm studies, in which patients with NMIBC were treated with second-line intravesical or systemic therapy after BCG failure. A minimum of eight patients were included in each treatment arm. Full papers were restricted to English language. Literature research and data analysis were assessed independently by two reviewers. Data on treatment response, recurrence, time to recurrence, progression and rate of cystectomy were collected and analysed. Results This systematic review included 42 publications with a total of 3521 patients (2371 BCG failures). Valrubicin, taxanes, gemcitabine, combination chemotherapy, thermochemotherapy, photodynamic therapy, combination of BCG and interferon and immunotherapies or targeted therapies were identified as conservative treatment options. For taxanes, gemcitabine and thermochemotherapy there is the highest evidence for a clinical meaningful response with minor toxicities. Conclusions Despite some promising response rates for taxanes, gemcitabine or thermochemotherapy, an evidence-based recommendation for treatment options superior to RC in patients failing BCG therapy cannot be made. The definition of BCG failure is still inconsistent and heterogeneous outcomes in patients with BCG failure have been reported. In order to identify effective conservative therapy options in patients failing BCG therapy, prospective trials with a standardised trial design are needed.