Purpose To analyze the efficacy, toxicity, and pattern of relapse after adjuvant cisplatin-based chemotherapy followed by three-dimensional irradiation and concomitant LV5FU2 chemotherapy (high-dose leucovorin and 5-fluorouracil bolus plus continuous infusion) in the treatment of completely resected high-risk gastric cancer. Methods and Materials This was a retrospective analysis of 52 patients with high-risk gastric cancer initially treated by total/partial gastrectomy and lymphadenectomy between January 2002 and June 2007. Median age was 54 years (range, 36–75 years). Postoperative treatment consisted of 5-fluorouracil and cisplatin chemotherapy. Adjuvant chemotherapy was followed by three-dimensional conformal radiotherapy in the tumor bed and regional lymph nodes at 4500 cGy/25 fractions in association with concomitant chemotherapy. Concomitant chemotherapy consisted of a 2-h infusion of leucovorin (200 mg/m²) followed by a bolus of 5-fluorouracil (400 mg/m²) and then a 44-h continuous infusion of 5-fluorouracil (2400–3600 mg/m²) given every 14 days, for three cycles (LV5FU2 protocol). Results Five-year overall and disease-free survival were 50% and 48%, respectively. Distant metastases and peritoneal spread were the most frequent sites of relapse (37% each). After multivariate analysis, only pathologic nodal status was significantly associated with disease-free and overall survival. Acute toxicities were essentially gastrointestinal and hematologic. One myocardial infarction and one pulmonary embolism were also reported. Eighteen patients had a radiotherapy program interruption because of acute toxicity. All patients but 2 have completed radiotherapy. Conclusion Postoperative cisplatin-based chemotherapy followed by conformal radiotherapy in association with concurrent 5-fluorouracil seemed to be feasible and resulted in successful locoregional control.