BACKGROUND. To identify the factors that contribute to poorer colon carcinoma survival rates for African Americans compared with Caucasians, the authors evaluated survival differences based on the histologic grade (differentiation) of the tumor. METHODS. All 169 African Americans and 229 randomly selected non-Hispanic Caucasians who underwent surgery during 1981-1993 for first primary sporadic colon carcinoma at the University of Alabama at Birmingham or its affiliated Veterans Affairs hospital were included in the current study. None of these patients received presurgery or postsurgery therapies. Recently, the authors reported an increased risk of colon carcinoma death for African Americans in this patient population, after adjustment for stage and other clinicodemographic features. The authors generated Kaplan-Meier survival probabilities according to race and tumor differentiation and multivariate Cox proportional hazards models to estimate hazard ratios (HR) with 95% confidence intervals (95% CI). RESULTS. There were no differences in the distribution of pathologic tumor stage between racial groups after stratifying by histologic tumor grade. Among patients with high-grade tumors, 54% of African Americans and 21% of Caucasians died within the first year after surgery (P = 0.007). African Americans with high-grade tumors were 3 times (HR = 3.05; 95% CI, 1.32-7.05) more likely to die of colon carcinoma within 5 years postsurgery, compared with Caucasians with high-grade tumors. There were no survival differences by race among patients with low-grade tumors. CONCLUSIONS. These findings suggested that poorer survival among African-American patients with adenocarcinomas of the colon may not be attributable to an advanced pathologic stage of disease at diagnosis, but instead may be due to aggressive biologic features like high tumor grades. © 2005 American Cancer Society.