CONTEXT: The European Association of Urology non-muscle-invasive bladder cancer (NMIBC) guidelines recommend that all low- and intermediate-risk patients receive a single immediate instillation of chemotherapy after transurethral resection of the bladder (TURB), but its use remains controversial. OBJECTIVE: To identify which NMIBC patients benefit from a single immediate instillation. EVIDENCE ACQUISITION: A systematic review and individual patient data (IPD) meta-analysis of randomized trials comparing the efficacy of a single instillation after TURB with TURB alone in NMIBC patients was carried out. EVIDENCE SYNTHESIS: A total of 13 eligible studies were identified. IPD were obtained for 11 studies randomizing 2278 eligible patients, 1161 to TURB and 1117 to a single instillation of epirubicin, mitomycin C, pirarubicin, or thiotepa. A total of 1128 recurrences, 108 progressions, and 460 deaths (59 due to bladder cancer [BCa]) occurred. A single instillation reduced the risk of recurrence by 35% (hazard ratio [HR]: 0.65; 95% confidence interval [CI], 0.58-0.74; p<0.001) and the 5-yr recurrence rate from 58.8% to 44.8%. The instillation did not reduce recurrences in patients with a prior recurrence rate of more than one recurrence per year or in patients with an European Organization for Research and Treatment of Cancer (EORTC) recurrence score ≥5. The instillation did not prolong either the time to progression or death from BCa, but it resulted in an increase in the overall risk of death (HR: 1.26; 95% CI, 1.05-1.51; p=0.015; 5-yr death rates 12.0% vs 11.2%), with the difference appearing in patients with an EORTC recurrence score ≥5. CONCLUSIONS: A single immediate instillation reduced the risk of recurrence, except in patients with a prior recurrence rate of more than one recurrence per year or an EORTC recurrence score ≥5. It does not prolong either time to progression or death from BCa. The instillation may be associated with an increase in the risk of death in patients at high risk of recurrence in whom the instillation is not effective or recommended. PATIENT SUMMARY: A single instillation of chemotherapy immediately after resection reduces the risk of recurrence in non-muscle-invasive bladder cancer; however, it should not be given to patients at high risk of recurrence due to its lack of efficacy in this subgroup.