Abstract Background Restorative proctocolectomy [RPC] without a defunctioning loop ileostomy [DLI] in patients with ulcerative colitis [UC] remains controversial. Aim To compare safety and efficacy of RPC with and without DLI in patients exclusively with UC. Methods A systematic review was performed according to PRISMA/MOOSE guidelines. Dichotomous variables were pooled as odds ratios [OR]. Continuous variables were pooled as weighted mean differences [WMD]. Quality assessment was performed using the Newcastle-Ottawa score [NOS]. Results A total of 20 studies [five paediatric and 15 adult] with 4550 UC patients [without DLI, n = 2370, 52.09%; with DLI, n = 2180, 47.91%] were eligible for inclusion. The median NOS was 8 [range 6–9]. There was no increased risk of anastomotic leak [AL] (OR 1.13, 95% confidence interval [CI]: 0.92, 1.39; p = 0.25), pouch excision [OR 1.01, 95% CI: 0.68, 1.50; p = 0.97], or overall major morbidity [OR 1.44, 95% CI, 0.91, 2.29; p = 0.12] for RPC without DLI, and this technique was associated with fewer anastomotic strictures [OR 0.45, 95% CI: 0.29, 0.68; p = 0.0002] and less bowel obstruction [OR 0.73, 95% CI: 0.57, 0.93; p = 0.01]. However, RPC without DLI increased the likelihood of pelvic sepsis [OR 1.68, 95% CI: 1.03, 2.75; p = 0.04] and emergency reoperation [OR 1.74, 95% CI: 1.22, 2.50; p = 0.002]. Conclusion RPC without DLI is not associated with increased clinically overt AL or pouch excision rates. However, it is associated with increased risk of pelvic sepsis and emergency reoperation. RPC without DLI is feasible, but should only be performed judiciously in select UC patient cohorts in high-volume, specialist, tertiary centres.