An adenocarcinoma of the appendix is a rare tumor, and so far only 130 cases have been reported worldwide. We report one patient with peritoneal seeding of an adenocarcinoma. A 51-year-old man was admitted to our hospital with the impression of intestinal obstruction. He had undergone an appendectomy 5 years ago due to acute appendicitis. At that time, postoperative histopathological analysis had revealed an adenocarcinoid tumor in the appendix. The patient had been told to visit our hospital for follow-up but he hadn't visited. When he finally visited our hospital diagnostic laparoscopy revealed the peritoneal seeding of a recurrent adenocarcinoma. A palliative right hemicolectomy was done to relieve the bowel obstruction. After recovering from operation, the patient was treated with the 5-fluoruracil, leucovorin, and oxaloplatin (FOLFOX). The patient was discharged in improved general condition with a future plan for regular cyclic chemotherapy.