The purpose of this study was to evaluate the impact of adjuvant chemotherapy on survival after surgery for T3N0 colon cancer. All patients with node-negative (N0) colon cancer with tumor invasion beyond the muscularis propria (T3) treated with colectomy between 1982 and 1995 at a single institution were included. Patients were divided into two groups depending on postcolectomy treatment with or without adjuvant chemotherapy. Groups were evaluated to determine perioperative and pathologic variables that could potentially influence outcome and surveillance data to determine disease-free and overall survival. In 253 patients with T3N0 colon cancer 226 remained under observation and 27 were treated with adjuvant chemotherapy. The groups were similar (P = not significant) when compared for tumor location, size, differentiation, number of nodes harvested, and transfusion requirements. Four of the 27 patients who received chemotherapy developed a recurrence (14.8%), whereas 22 of the 226 observation patients developed a recurrence (9.7%). Disease-free survival for the chemotherapy group at 5 years was 84 per cent and for the observation group 87 per cent. Statistical analysis (Mantel-Cox) showed no significant difference between the groups on the basis of survival (P = 0.3743). We conclude that resection alone is a highly effective treatment for T3N0 colon cancer leaving limited opportunity for adjuvant chemotherapy to significantly impact survival. Adjuvant chemotherapy for T3N0 colon cancer patients should be limited to patients enrolled in clinical trials designed to identify subgroups of T3N0 colon cancer patients at a survival disadvantage or less toxic adjuvant chemotherapies.