Background: It is well established that age and comorbidities have significant impact on adjuvant chemotherapy delivery to stage III colon cancer patients. This study examines differences in the hospital and surgeon-specific probabilities of adjuvant therapy delivery to stage III colon cancer patients by comorbidity burden and age. Methods: Patients who underwent surgery for stage III colon cancer from 2004-2013 were included from the New York State Cancer Registry and the Statewide Planning and Research Cooperative System. Comorbidity burden was defined with the Charlson Comorbidity Index (CCI). Multilevel logistic regressions characterized variation in adjuvant chemotherapy delivery among individual hospitals and surgeons by CCI and age. Results: 11575 patients met inclusion criteria, of which 59% received adjuvant therapy. Younger age, lower CCI, and high volume surgeons/hospitals were associated with delivery of adjuvant therapy (p < 0.01). Median time to chemotherapy was 43 days among CCI = 0 vs 48 among CCI≥2. The risk adjusted hospital and surgeon-specific probabilities of adjuvant delivery decreased with increasing CCI and age. The proportion of variation attributable to surgeons, vs hospitals, increased with CCI and age. Hospital variation between the highest and lowest hospitals increased from a 6-fold difference among CCI = 0 to an 11 fold difference among CCI≥2. Surgeon variation increased from a 14-fold difference among CCI = 0 to a 40 fold difference among CCI≥2. Conclusions: Variation in adjuvant chemotherapy delivery to stage III colon cancer patients increased with higher comorbidity burden and age. While a larger proportion of variation is attributable to surgeons among patients with the highest CCI and the most elderly, the vast majority of the variation is related to hospital factors. Even taking into account that some patients may be unfit for adjuvant therapy, this variation in treatment is alarmingly high.