A 63-year-old man was admitted with an abdominal mass in the right lower quadrant. The tumor was diagnosed as mucocele of the appendix after admission and surgically removed. The appendix containing gelatinous mucus with numerous round bodies was distended to the size of an egg. Therefore, a diagnosis of myxoglobulosis was postoperatively made. This is a rare disease and the diagnosis has been preoperatively made in none of patients in Japan. The present case could present an echographic pattern characteristic of this cyst. Studies on all available echograms from previous patients could provide information necessary for preoperative diagnosis of myxoglobulosis.