PURPOSE: This study was designed to determine the prognosis of patients with synchronous colon primary tumors. METHODS: An 18-year, multi- institutional database of 4,878 colon cancer patents was reviewed, and patients with synchronous tumors were identified. Survival for each group was calculated by the Kaplan-Meier method and compared using log-rank analysis. RESULTS: There were 160 patients (3.3 percent) with 339 synchronous tumors. Eight percent of these patients had more than two tumors at the time of diagnosis. TNM staging of all synchronous tumors was 12 percent Stage 0, 41 percent Stage I, 21 percent Stage II, 16 percent Stage III, and 7 percent Stage IV. Based on highest stage lesion, 1 percent of patients were at Stage 0, 28 percent Stage I, 33 percent Stage II, 25 percent Stage III, and 11 percent Stage IV. Disease-specific five year survival by highest stage was 87 percent for Stage O or I, 69 percent for Stage II, 50 percent for Stage III, and 14 percent for Stage IV (all differences significant by log-rank test). These 'highest stage' survivals for patients with synchronous tumors were not significantly different from survival of patients with same stage solitary tumors in our database or from survival of patients with solitary colon cancer in national tumor databases. CONCLUSION: For patients with synchronous colon cancers, survival is the same as for patients with solitary colon tumors on a stage-for-stage basis, when highest stage synchronous tumor is considered.