Spontaneous regression of malignant tumour is a rare phenomenon. This report describes such an occurrence in a gastric large cell neuroendocrine carcinoma of a 77-year-old man. The patient presented with dyspepsia, and biopsy of the fungating mass in the cardia showed a high grade neuroendocrine carcinoma. The pre-operative biopsy taken after 3 months showed chronic inflammation and cytomegalovirus inclusions, but no tumour. In the gastrectomy specimen, no residual tumour was found. Instead, there were foamy histiocytes, chronic inflammatory cells and fibrovascular tissue splitting apart the muscularis propria. In addition, there was ganglionitis involving the myenteric plexus, even in areas of the stomach away from the inflamed site. Chemotherapy, radiotherapy or alternative medicine (including herbal medicine) had not been given. We postulate that cytomegalovirus infection initiated a cross-autoimmune reaction against neuronal cells, and this reaction "unintentionally" eliminated the carcinoma cells which also expressed neural antigens.