Urgent-start peritoneal dialysis (PD), defined as initiation of PD within two weeks of catheter insertion, has been emerging as an alternative mode of dialysis initiation for patients with chronic kidney disease (CKD) requiring urgent dialysis without established permanent dialysis access. Recently, several small studies have reported comparable patient outcomes between urgent-start and conventional-start PD. To examine the benefits and harms of urgent-start PD compared with conventional-start PD in adults and children with CKD requiring long-term kidney replacement therapy. We searched the Cochrane Kidney and Transplant Register of Studies up to 25 May 2020 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal, and ClinicalTrials.gov. For non-randomised controlled trials, MEDLINE (OVID) (1946 to 27 June 2019), EMBASE (OVID) (1980 to 27 June 2019), Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov (up to 27 June 2019) were searched. All randomised controlled trials (RCTs) and non-RCTs comparing the outcomes of urgent-start PD (within 2 weeks of catheter insertion) and conventional-start PD ( ≥ 2 weeks of catheter insertion) treatment in children and adults CKD patients requiring long-term dialysis were included. Studies without a control group were excluded. Data were extracted and quality of studies were examined by two independent authors. The authors contacted investigators for additional information. Summary estimates of effect were examined using random-effects model and results were presented as risk ratios (RR) with 95% confidence intervals (CI) as appropriate for the data. The certainty of evidence for individual outcome was assessed using the GRADE approach. A total of 16 studies (2953 participants) were included in this review, which included one multicentre RCT (122 participants) and 15 non-RCTs (2831 participants): 13 cohort studies (2671 participants) and 2 case-control studies (160 participants). The review included unadjusted data for analyses due to paucity of studies reporting adjusted data. In low certainty evidence, urgent-start PD may increase dialysate leak (1 RCT, 122 participants: RR 3.90, 95% CI 1.56 to 9.78) compared with conventional-start PD which translated into an absolute number of 210 more leaks per 1000 (95% CI 40 to 635). In very low certainty evidence, it is uncertain whether urgent-start PD increases catheter blockage (4 cohort studies, 1214 participants: RR 1.33, 95% CI 0.40 to 4.43; 2 case-control studies, 160 participants: RR 1.89, 95% CI 0.58 to 6.13), catheter malposition (6 cohort studies, 1353 participants: RR 1.63, 95% CI 0.80 to 3.32; 1 case-control study, 104 participants: RR 3.00, 95% CI 0.64 to 13.96), and PD dialysate flow problems (3 cohort studies, 937 participants: RR 1.44, 95% CI 0.34 to 6.14) compared to conventional-start PD. In very low certainty evidence, it is uncertain whether urgent-start PD increases exit-site infection (2 cohort studies, 337 participants: RR 1.43, 95% CI 0.24 to 8.61; 1 case-control study, 104 participants RR 1.20, 95% CI 0.41 to 3.50), exit-site bleeding (1 RCT, 122 participants: RR 0.70, 95% CI 0.03 to 16.81; 1 cohort study, 27 participants: RR 1.58, 95% CI 0.07 to 35.32), peritonitis (7 cohort studies, 1497 participants: RR 1.00, 95% CI 0.68 to 1.46; 2 case-control studies, participants: RR 1.09, 95% CI 0.12 to 9.51), catheter readjustment (2 cohort studies, 739 participants: RR 1.27, 95% CI 0.40 to 4.02), or reduces technique survival (1 RCT, 122 participants: RR 1.09, 95% CI 1.00 to 1.20; 8 cohort studies, 1668 participants: RR 0.90, 95% CI 0.76 to 1.07; 2 case-control studies, 160 participants: RR 0.92, 95% CI 0.79 to 1.06). In very low certainty evidence, it is uncertain whether urgent-start PD compared with conventional-start PD increased death (any cause) (1 RCT, 122 participants: RR 1.49, 95% CI 0.87 to 2.53; 7 cohort studies, 1509 participants: RR 1.89, 95% CI 1.07 to 3.3; 1 case-control study, 104 participants: RR 0.90, 95% CI 0.27 to 3.02; very low certainty evidence). None of the included studies reported on tunnel tract infection. In patients with CKD who require dialysis urgently without ready-to-use dialysis access in place, urgent-start PD may increase the risk of dialysate leak and has uncertain effects on catheter blockage, malposition or readjustment, PD dialysate flow problems, infectious complications, exit-site bleeding, technique survival, and patient survival compared with conventional-start PD.