CONTEXT: Initial treatment for most bladder cancers (BCs) involves transurethral resection (TUR) or tumours. Often more cancer is found after the initial treatment in around half of patients, requiring a second resection. Repeat transurethral resection (reTUR) is recommended for high-risk, non-muscle-invasive bladder cancer (NMIBC) to remove any residual disease and improve cancer outcomes. OBJECTIVE: To systematically review the practice and therapeutic benefit of an early reTUR for high-risk NMIBC. EVIDENCE ACQUISITION: A systematic review of original articles was performed using PubMed/Medline and Web of Science databases in December 2016 (initial) and October 2017 (final). We searched the references of included papers. EVIDENCE SYNTHESIS: We screened 15 209 manuscripts and selected 31 detailing 8409 persons with high-grade Ta and T1BC for inclusion. Detrusor muscle was found at initial TUR histology in 30-100% of cases. Residual tumour at reTUR was found in 17-67% of patients following Ta and in 20-71% following T1 cancer. Most residual tumours (36-86%) were found at the original resection site. Upstaging occurred in 0-8% (Ta to ≥T1) and 0-32% (T1 to ≥T2) of cases. Conflicting data report the impact of reTUR on subsequent recurrence and cancer-specific mortality. Recurrence for Ta was 16% in the reTUR group versus 58% in the non-reTUR group. For T1, recurrence ranged from 18% to 56%, but no clear trend was identified between reTUR and control. No clear relationship between reTUR and progression was found for Ta, although for T1 rates were higher in the non-reTUR group in series with control populations (5/6 studies). Overall mortality was slightly reduced in the reTUR group in two studies with controls (22-30% vs 26-36% [no reTUR]). CONCLUSIONS: Residual tumour is common after TUR for high-risk NMIBC. The reTUR helps in the diagnosis of this residual cancer and may improve outcomes for cancers initially staged as T1. PATIENT SUMMARY: Some bladder cancers (BCs) are aggressive but confined to the bladder surface. Initial treatment includes endoscopic resection. More cancer is found after the initial treatment in approximately half of patients. In the aggressive but confined group of BC, a second resection, a few weeks after the first, may help find this residual cancer and improve outcomes, although the evidence quality for this is weak.