We report a patient with abdominal pain, diarrhea, and edema of the small intestine all of which disappeared after resection of an ovarian mucinous cystadenoma of borderline malignancy. Preoperatively, the serum gastrin level was high and it decreased to normal afterwards; subsequent immunohistochemical studies of the tumor revealed cytoplasmic hormone granules containing gastrin-like immunoreactivity. We believe that the symptoms in our patient were the result of an ectopic ovarian gastrin-producing tumor.