Because of its safety and treatment effectiveness, the popularity of radiofrequency ablation (RFA) for the treatment of hepatocellular carcinoma (HCC) has gradually increased. However, some serious complications of RFA such as hepatic infarction, bowel perforation, and tumor seeding have been reported. Recently, we experienced a case of diaphragmatic hernia after RFA for HCC. A 61-year-old man with alcoholic cirrhosis was diagnosed with a 1.0 cm sized HCC in segment (S) 5 and a 1.3 cm sized HCC in S 8 of the liver. He was treated by transarterial chemoembolization and RFA. After RFA, an abdominal CT revealed a diaphragmatic defect with herniating mesentery. Twenty-two months after the RFA, the chest CT showed the diaphragmatic defect with herniating colon and mesentery. Because he had no symptoms, and surgical repair for the diaphragmatic hernia would be a high risk operation for him, we decided to treat the patient conservatively. For its great rarity, we report this case with a review of the literature. (Korean J Gastroenterol 2013;62:174-178)