Of the original group of 4962 patients with node-positive colon cancer, 194 (3.91%) received chemotherapy that did not include 5-FU. These patients were excluded from further analysis. Table 1 shows the demographic and clinical characteristics of the remaining 4768 patients and the proportions treated with 5-FU. Overall, 52% of patients received 5-FU. Table 2 compares treated and untreated patients with respect to age, year of diagnosis, ethnicity, sex, urban residence, specific SEER cancer registry site, number of lymph nodes involved with tumor, tumor grade, extent of disease, and comorbid disease status. All of these covariates were predictors of treatment with 5-FU and were unequally distributed between the treated and untreated groups. With adjustment for propensity score, all covariates (except for age) were balanced within each stratum. Only 11% of patients in quintile 1 (mean age, 87 years) but 83% of those in quintile 5 (mean age, 69 years) were treated (Table 3). Therefore, age was strongly associated with treatment.