The significance of backwash ileitis (BWI) relating to the risk of colon neoplasia in ulcerative colitis (UC) patients is controversial.

We investigated the association between BWI and the presence of colon neoplasia in the colectomy specimen.

From 4,198 UC patients in a prospectively maintained pouch database from 1983 to 2011, patients with extensive colitis and BWI (n = 178) in proctocolectomy were compared with 537 controls [extensive colitis (n = 385) and left-sided colitis (n = 152)] without ileal inflammation.

Colon neoplasia (colon dysplasia and/or colon cancer) was seen in 32 (18 %) patients with BWI in contrast to 45 (11.7 %) with extensive colitis and 13 (8.6 %) with left-sided colitis alone (p = 0.03). Of those with BWI, colon cancer was seen in 10 patients (5.6 %), while low grade and high grade dysplasia were seen in 7 (3.9 %) and 15 (8.4 %) patients respectively. On multivariate analysis, the presence of BWI with extensive colitis [odds ratio (OR) = 3.53; 95 % confidence interval (CI) 1.01–12.30, p = 0.04], presence of primary sclerosing cholangitis (PSC) (OR = 5.79, 95 % CI 1.92–17.40, p = 0.002) and moderate to severe disease activity at UC diagnosis (OR 4.29, 95 % CI 2.06–9.01, p < 0.001) were associated with an increased risk for identifying any colon neoplasia. For colon cancer, the presence of PSC (OR = 11.30, 95 % CI 1.54–80.9, p = 0.01) was the only factor independently associated with an increased risk.

The presence of BWI with extensive colitis was associated with the risk of identifying colon neoplasia but not cancer alone in the proctocolectomy specimen.