Aim Patients with rectal cancer often undergo faecal diversion, yet the existing literature cursorily reports renal sequelae by the type of ostomy. We aimed to determine whether the presence of an ileostomy or colostomy was associated with postoperative renal morbidity. Methods We identified patients with rectal cancer undergoing elective resection with primary anastomosis without diversion, with an ileostomy and with a colostomy by 21 possible procedures in the colectomy‐ and proctectomy‐specific National Surgical Quality Improvement Program files. The odds of major renal events (renal failure dialysis initiated or progressive renal insufficiency >2 mg/dl increase in creatinine without dialysis), progressive renal insufficiency alone and readmissions were assessed using propensity score weighting and logistic regression. Results Of 15 075 patients (63.7% Stage II–III, 85.7% creatinine values obtained ≤30 days preoperatively), 37.7% were not diverted, 39.5% had an ileostomy and 22.9% a colostomy. Compared to non‐diverted patients, diversion was associated with major renal events (ileostomy, odds ratio OR 2.1, 95% confidence interval CI 1.6–2.9; colostomy, OR 1.8, 95% CI 1.3–2.5), progressive renal insufficiency (ileostomy, OR 2.5, 95% CI 1.7–3.5; colostomy, OR 2.0, 95% CI 1.4–2.9), readmissions for renal failure (ileostomy, OR 3.2, 95% CI 2.1–5.0; colostomy, OR 2.5, 95% CI 1.6–4.1) and readmissions for fluid/electrolyte abnormalities (ileostomy, OR 2.3, 95% CI 1.6–3.3; colostomy, OR 1.8, 95% CI 1.2–2.6). Conclusion Diverting ostomies after elective rectal cancer resection are strongly associated with renal morbidity. The decision to divert is complex, and it is unclear whether select patients may benefit from a colostomy from a renal perspective.