Aims: To determine whether serosal invasion (SI) and/or extramural venous invasion (VI) could be more frequently identified on review of Dukes' stage B colonic carcinoma resection specimens and whether the revised findings correlated with clinical outcome.Methods and results: The original histology slides from 82 patients with Dukes' stage B colonic carcinoma were reviewed specifically to identify tumours showing SI and/or VI. All tumours were initially reported to be negative for both pathological parameters. The selected cases included 35 patients who died of carcinoma within 5 years of surgery and 47 patients with a minimum of 5-years' postoperative survival. The review was blinded to the original histopathology reports and to clinical follow-up data. SI and/or VI were identified in 26 cases (32%). Fourteen of 18 patients with SI, 8/12 patients with VI and all four patients with both adverse histological features died of carcinoma.Conclusions: Review of routinely sampled and stained colonic carcinoma resection specimens increased the proportion of cases classified as positive for SI and/or VI. The revised assessment correlated with patient outcome. Reliable identification of these features may permit stratification of high-risk patients with Dukes' stage B colonic cancer who could benefit from adjuvant treatment.