The simultaneous association of gastric carcinoma with omental mucosa-associated lymphoid tissue (MALT) lymphoma is a rare event that has not been reported previously. We focused on the hypothetic pathogenetic mechanisms, diagnosis and treatment of this rare condition. A 55-year-old woman with Helicobacter pylori infection underwent distal gastrectomy in our hospital. Three independent early gastric cancers and a mass near the cecum were diagnosed preoperatively. Pathological review of the resected stomach showed three independent early signet ring cell gastric carcinomas, and the mass in the omentum near the cecum was shown to be omental MALT lymphoma. Due to the nature of the patient's disease, she was started on medical eradication of H. pylori. Synchronous gastric adenocarcinoma and omental MALT lymphoma is a rare event. Special attention given to H. pylori-associated gastric cancer patients can avoid misdiagnosis and lead to adequate treatment.