The dichotomous distribution of gastrinomas. Our experience with 47 sporadic gastrinomas suggests that no less than 85% of these tumors are located to the right of the superior mesenteric artery. This finding is unexpected because approximately 75% of insulinomas and glucagonomas are located to the left of the superior mesenteric artery. All of our extrapancreatic gastrinomas have been located to the right. These observations prompted us to determine if other extrapancreatic gastrinomas were also predominantly located to the right side. We searched the world's literature and found 10 cases of ovarian gastrinomas and one case of a renal gastrinoma. Nine of these remote extrapancreatic gastrinomas were located on the right side. This distribution of remote extrapancreatic gastrinomas is similar to our experience with peripancreatic gastrinomas. This unexpected right-sided preponderance of both remote and peripancreatic gastrinomas suggests a common origin for both. 