The diagnosis of vasoactive intestinal polypeptide-secreting tumor (VIPoma) was established in two boys on the basis of watery diarrhea with hypokalemia, elevated plasma levels of vasoactive intestinal polypeptide (VIP) (range of 55–94 pmol/L), and presence of a tumor of the left adrenal gland. Despite celiac angiography, VIP estimation in blood samples taken from different parts of the body, and exploratory laparotomy, localization of the tumor in one childin vivowas unsuccessful. In the other boy, computed tomography revealed a large tumor in the left adrenal gland. Following the removal of the tumor, diarrhea ceased, and 10 days after surgery, the plasma level of VIP was 5 pmol/L. Histologically, the tumors in the two boys were found to be ganglioneuromas. The diagnosis of VIPoma is simple but localization can be very difficult. Surgical removal of VIPoma is often rewarding.