Background: The optimal adjuvant treatment regimen for stage III CRC patients aged ≥70 years remains unclear. Subgroup analyses of randomised trials support the use of single agent fluoropyrimidines (FP) but no survival benefit has been observed for the addition of oxaliplatin. This study assessed rates of AC use in elderly patients with stage III CRC, analysed reasons why elderly patients did not receive AC and compared disease free survival (DFS) between those who did and did not receive AC. Methods: Data was analysed from the ACCORD-CRC registry, which prospectively collects treatment and outcome data from patients with CRC in Australia. All patients aged ≥70 years with resected stage III CRC from seven institutions between January 2005 and December 2018 were included. Where patients did not receive AC, reasons for this were documented prospectively. Using univariate analysis, baseline demographics and clinicopathological variables were compared between patients who were and were not offered AC. Differences were defined as statistically significant if a two-tailed p value was < 0.05. DFS was defined as time from surgical resection to time of recurrence and cases of death without recurrence were censored at the time of death. Results: Data was obtained for 685 patients; median age was 78 years (range 70-97). AC was offered to 72% of patients; these patients were significantly more likely to be aged 70-74y (34% vs 12%, p < 0.0001), have an ECOG score of 0-1 (88% vs 57%, p < 0.0001), have proficient mismatch repair (pMMR) (87 vs 75%, p = 0.01) and T1-3 tumours (74% vs 65%, p = 0.02) compared to patients not offered AC. Nodal status and tumour differentiation did not differ significantly. 15% of patients offered AC declined systemic treatment. The most frequent documented reasons for not offering AC were age plus comorbidities, followed by comorbidities alone and age alone (42%, 29% and 23%, respectively). Of the patients who commenced AC, 27% received oxaliplatin-FP. These patients were significantly more likely to be aged 70-74y (71% vs 28%, p < 0.0001), have an ECOG score of 0-1 (94% vs 87%, p = 0.04), have N2 disease (39% vs 26%, p = 0.02) and poorly differentiated tumours (42% vs 29%, p = 0.02) compared to those receiving FP alone. T-stage and MMR status did not differ significantly. After median follow up of 32 months, the 3-year DFS rate was higher for patients who received AC compared to those who did not (71% vs 64%; HR 0.72, p = 0.046) but no significant difference was observed for the addition of oxaliplatin (75% vs 69%; HR 0.76, p = 0.18) compared to FP alone. Conclusions: In this real world cohort, approximately 75% of elderly patients with stage III CRC were offered AC. Younger age, better performance status, pMMR and lower T stage were significantly associated with physicians offering elderly patients AC. Those who received AC had improved DFS compared to those who did not.