A total of 122 specimens of colorectal cancer were re-assessed in relation to the reporting of invasive growth pattern (expanding vs. infiltrating) and presence or absence of peritumoral lymphocytic infiltrate as used in the Jass prognostic classification. Jass agreed with 69% of cases reported as infiltrating and 90% of reported as expanding. This parameter was distributed similarly amongst Dukes B and C cases in the original assessment (P = 0.27), whereas in the reviewed data infiltrating cases were more likely to be staged as Dukes C (P = 0.04). Jass agreed with 44% of lymphocyte present and 94% of lymphocyte absent assessments. The original lymphocyte assessments showed no significant differences in distribution between Dukes A and B cases (P = 0.12) or B and C cases (P = 0.75), whereas the reviewed data showed significant differences for A vs. B (P = 0.015) and B vs. C cases (P = 0.0025). Criteria for assessment were circulated to eight observers who revisited 20 of the cases in which there was disagreement. Consensus agreement with Jass was achieved in nine of 10 cases for invasive growth pattern and seven of 10 cases for lymphocyte infiltration (with two being evenly split). Most observers showed at least fair levels of agreement with Jass and some achieved excellent levels of agreement. This study indicates that assessment of criteria used in the Jass prognostic system for colorectal cancer is less than optimal in routine practice, but is improved through the provision of simple guidelines.