Background Radical cystectomy (RC) is the primary surgical treatment for muscle-invasive urothelial carcinoma of the bladder. This major operation is associated with an extended hospital stay, a prolonged recovery period and major complications. Nutritional interventions have been shown to be beneficial in some people with other types of cancer and may be of value in this setting too. Objectives To assess the effects of perioperative nutrition in participants undergoing radical cystectomy for the treatment of bladder cancer. Search methods We performed a comprehensive search using multiple databases (Evidence Based Medicine Reviews, MEDLINE, Embase, AMED, CINAHL), trials registries, other sources of grey literature, and conference proceedings published up to June 30, 2018, with no restrictions on the language or status of publication. Selection criteria Perioperative nutrition for the treatment of bladder cancer by radical cystectomy 1 / 64 We included parallel-group randomised controlled trials (RCTs) of adults undergoing RC for bladder cancer. The intervention was any perioperative nutrition support. Data collection and analysis Two review authors independently assessed studies for inclusion at each stage and undertook data extraction and risk of bias and GRADE assessments of the quality of evidence. Primary outcomes were postoperative complications at 90 days and length of hospital stay. 90-day Mortality was the predefined secondary outcome. When 90 day outcome data was not available, we reported 30 day data. Main results Eight trials were identified including 500 participants. Six trials were conducted in the USA and two in Europe. 1. Parenteral nutrition (PN) versus oral nutrition: based on one study with 157 participants, PN may increase postoperative complications within 30 days (risk ratio (RR) 1.40, 95% CI (confidence intervals) 1.07 to 1.82; low quality of evidence). We downgraded for serious study limitations (unclear risk of selection, performance and selective reporting bias) and serious imprecision. This correspond to 198 more complications per 1000 participants (95% CI 35 more to 405 more). Length of stay may be similar (mean difference (MD) 0.5 days higher; no CI reported, low quality of evidence). We downgraded for serious study limitations (unclear risk of selection, performance and selective reporting bias) and serious imprecision. 2. Immuno-enhancing nutrition versus standard nutrition: based on one study including 29 participants, immunoenhancing nutrition may reduce 90 day postoperative complications (RR 0.31, 95% CI 0.08 to 1.23; low quality of evidence). These findings correspond to 322 fewer complications per 1000 participants; 95% CI 429 fewer to 107 more). Length of stay may be similar (MD 0.20 days, 95% CI 1.69 lower to 2.09 higher; low quality of evidence). We downgraded both outcomes for very serious imprecision. 3. Preoperative oral nutritional support versus normal diet: based on one study including 28 participants, we are very uncertain if preoperative oral supplements reduces pos...