BACKGROUND Splenic cysts are rare. Most are due to previous trauma, infection, or infarction. They are generally handled by laparoscopic surgical removal if they are larger than 5 cm. However, very large cysts may require splenectomy. Another factor in the choice of therapy is the patient's underlying condition. We present the case of a giant splenic cyst in a woman 1 year after a renal transplant. CASE REPORT A 28-year-old woman presented with acute abdominal pain and nausea. One year before, she had received an ABO-identical living donor renal transplantation from her father, and was maintained on oral tacrolimus and prednisolone. A CT scan with contrast showed enteric ileus and an abnormal position of the spleen, which was involved by a cyst measuring 12×12.5×9 cm. A nasogastric tube, and later a small bowel tube, were inserted to decompress the ileus. The patient underwent laparotomy 11 days after admission. We confirmed an internal hernia with volvulus due to migration of the spleen; however, there was no evidence of necrosis. The patient was treated with splenectomy and reduction of the hernia. There were no complications. CONCLUSIONS This was a very unusual emergency following renal transplantation. Splenectomy has been performed in the past for immunosuppression in cases of donor ABO-incompatibility. We therefore considered that it would be more expedient to remove the spleen than to remove the cyst and perform splenopexy.