We have experienced a case of incarcerated umbilical hernia in an adult. A 44-year-old woman was referred to the hospital because of a painful umbilical tumor, with the size of ping-pong ball which appeared 4 years before admission, but was let alone. The tumor in the umbilical region was painful and red. Abdominal computed tomography showed a bowel mass in the fat of the abdominal wall. The leukocyte count was elevated. A diagnosis of incarcerated umbilical hernia was made, and an emergency surgery was performed. The incarcerated small intestine about 5cm in lenght did not require resection and it was reduced because this operation was done several hours after the onset of incarceration. The postoperative course was uneventful and she was discharged very much improved 9 days afer the operation. In a review of the literature, incarcerated umbilical hernia in adults is rare and 27 cases including our case have been reported in Japan in the recent 10 years.