Purpose. Our primary objective was to compare cancer-directed treatments provided to patients with 1st versus 2nd primary diagnosis of colorectal cancer. Methods. We used Medicaid and Medicare administrative data merged with a state population-based tumor registry to extract a sample of patients age 66 years and older with a first primary colorectal tumor and patients diagnosed with a second primary colorectal tumor. Patients with both first and second colorectal cancers were excluded. The study period was between January 1996 and December 2000 (n=6539). The outcomes of interest were: 1) receipt of any treatment; 2) receipt of resection for those treated; and 3) receipt of adjuvant chemotherapy or radiation following resection for regional stage disease. All models were estimated using multivariable logistic regression. Results. Controlling for demographic characteristics, dual eligibility, comorbidity, stage of colorectal cancer, and death during the initial treatment period, patients with a 2nd primary colorectal cancer were less likely to receive treatment within 6 months following diagnosis than those with a 1st primary colorectal cancer (OR=0.66; 95% CI: 0.47, 0.93). Statistically significant differences were not observed among treated patients who received a resection. Among resected patients with regional disease, patients with a 2nd primary colorectal cancer were less likely to receive adjuvant chemotherapy or radiation compared to patients with a 1st primary colorectal cancer (OR=0.28; 95% CI: 0.17, 0.46). Conclusions. Cancer survivors are at elevated risk for 2nd primary tumors following the treatment for their 1st primary tumor. Second primary malignancies among this high-risk group account for up to16% of all cancer incidence. Although evidence-based guidelines are in place for follow-up care and screening for many cancers, evidence-based guidelines for treatment of second malignancies are remarkably absent. We found that patients with a 2nd primary colorectal cancer are treated less aggressively than patients with a 1st primary colorectal cancer. This practice pattern may result in poor symptom control and survival for patients with 2nd primary cancers. Our study suggests that there is considerable room for improvement in the clinical management of the growing population of cancer survivors with 2nd primary cancers.