Background: Patients (pts) with multiple synchronous colon cancer primaries (MCPs) constitute a unique subset of pts with colon cancer. However, there are limited published studies about these pts. The objective of this study is to compare the characteristics and outcomes of pts with MCPs to those with single colon cancer primaries (SCPs) using the largest study population to date. Methods: Data was obtained from the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2015. Pts with synchronous MCPs were included and were matched 1:3 with pts with SCPs based on the Coarsened Exact Matching method for age, gender, and race. Only patients with multiple synchronous primaries were included (time since index = 0 months). We excluded pts with a lag time since diagnosis of index primary of 1 month or more. Univariate (UNA) and multivariable (MVA) analyses were performed to identify factors associated with patient outcomes. Kaplan-Meier analyses and Cox proportional hazards models were used to assess the association between tumor/patient characteristics and overall survival (OS). Results: A total of 3322 pts with MCPs and 9966 pts with SCPs were identified. Median age was 71 years. Majority were male (51.5%) and White (80.1%). 73.4% and 69.6% of pts had 12 or more lymph nodes examined for the MCPs and SCPs cohorts, respectively. The SCPs cohort included more T4 stage and more well- and moderately-differentiated histology. OS was significantly shorter in MCPs compared to SCPs (HR 1.29; 1.22-1.36; p < 0.001), with a 5- and 10-year OS rate of 47.8% and 28.2% for the MCPs and 56.4% and 41.6% for the SCPs, respectively, for all stages combined. In the MCPs cohort, the use of adjuvant chemotherapy was associated with an improved survival in AJCC stages II, III, and IV but not stage I. Conclusions: This is the largest study evaluating the impact of MCPs on outcomes. Across stages II to IV, pts with MCPs have a shorter survival than those with SCPs. Pts with stage II MCPs who receive adjuvant chemotherapy derive a survival benefit. Current guidelines do not list multiple synchronous primaries as a high-risk feature for stage II.