['Previous studies suggest that long-term mortality is increased in patients who undergo splenectomy during surgery for colorectal cancer. The reason for this association remains unclear.', 'The purpose of this study was to investigate the association between inadvertent splenectomy attributed to iatrogenic lesion to the spleen during colorectal cancer resections and long-term mortality in a national cohort of unselected patients.', 'This was a retrospective, nationwide cohort study.', 'Data were collected from the database of the Danish Colorectal Cancer Group and merged with data from the National Patient Registry and the National Pathology Databank.', 'Danish patients with colorectal cancer undergoing curatively intended resection between 2001 and 2011 were included in the study.', 'The primary outcome was long-term mortality for patients surviving 30 days after surgery. Secondary outcomes were 30-day mortality and risk factors for inadvertent splenectomy. Multivariable and propensity-score matched Cox regression analyses were used to adjust for potential confounding.', 'In total, 23,727 patients were included, of which 277 (1.2%) underwent inadvertent splenectomy. There was no association between inadvertent splenectomy and long-term mortality (adjusted HR = 1.15 (95% CI, 0.95-1.40); p = 0.16) in the propensity score-matched model, whereas 30-day mortality was significantly increased (adjusted HR = 2.31 (95% CI, 1.71-3.11); p < 0.001). Inadvertent splenectomy was most often seen during left hemicolectomy (left hemicolectomy vs right hemicolectomy: OR = 24.76 (95% CI, 15.30-40.06); p < 0.001).'] Does inadvertent Splenectomy During Resection for Colorectal Cancer Increase Long-term Mortality in a Propensity Score Model : A Nationwide Cohort Study?