A 36-year old woman underwent upper gastrointestinal examination during a routine medical examination, which revealed an abnormality (Fig. 1a). She was admitted for further examination. She had no symptoms and her abdomen showed no obvious abnormality with palpation. Computed tomographic scan revealed an abdominal low-density tumor, which measured 8 cm in diameter, with partial calcification close to the stomach and spleen (Fig. 1b). She had no history of significant abdominal trauma. Results of physical and laboratory examinations were normal except for elevation of serum CA19-9 (carbohydrate antigen 19-9) levels of 244.4 U/ml. Surgical exploration suggested that a huge tumor originated from the spleen. Because malignancy and risk of rupture could not be denied, she underwent splenectomy. The excised specimen was a cystic lesion measuring 8.5 × 7.5 × 5.5 cm with necrosis and bleeding (Fig. 1c). Histopathologically, the removed specimen showed a unicystic lesion surrounded by splenic tissue with marked fibrosis and calcification (Fig. 2a). This cyst had eosinophilic contents with cell debris, cholesterol crystals and a few inflammatory cells. Although lining epithelium had been partially effaced, the cyst wall was mostly covered with thin, two to three-layered non-keratinizing stratified squamous epithelium having an intercellular bridge. A few ciliated cells were observed in the surface (Fig. 2a, inset). Immunohistochemically, the lining epithelium showed a full thickness positive reaction to both CK14 (Fig. 2b) and CK19 (Fig. 2c), and the upper half of the epithelium was positive for CA19-9 (Fig. 2d). This case was diagnosed as epidermoid cyst of the spleen. After one month of follow-up, the patient was in good clinical condition. Splenic cysts are classified into true cysts and pseudocysts, based on the presence or absence of lining epithelium. Among true splenic cysts, epidermoid cysts account for 90%. Even if true splenic cysts are benign, there are cases that show elevation of serum CA19-9. This condition can be explained by the CA19-9 positive cells that seem to produce this glycoprotein. CA19-9 will flow into blood if internal pressure of the cyst rises. There are various opinions on the origin of the cyst. In general, CK14 is a marker of stratified squamous epithelium, while CK19 is a marker of simple epithelium. In this case, the epithelium has both characteristics of simple and stratified squamous epithelium. The presence of CK19 and CA19-9 positive cells give us the impression that squamous metaplasia occurred in simple epithelium aberrantly embedded in the developing stage.