Meckel's diverticulum, which is the most common congenital anomaly of the gastrointestinal tract, occurs when the vitelline duct persists past the 7th week of gestation. Although complications may occur in 8% to 22% of patients with Meckel's diverticula, adenocarcinoma is very uncommon. We describe a patient with early gastric cancer who was incidentally found to have a superficial adenocarcinoma arising from ectopic gastric mucosa within a Meckel's diverticulum. To the best of our knowledge, synchronous gastric adenocarcinoma in a patient with Meckel's diverticulum has not been previously reported.