A 58-year-old man, who had presented with a large cyst between the pancreatic tail and splenic hilum 6 years previously, was referred to our hospital with exacerbation of abdominal distention. Computed tomography revealed a well-demarcated, unilocular cyst, with a beak sign for the pancreas, without wall thickening or nodules suggestive of a non-neoplastic cyst. Compared with 6 years previously, the cyst had increased in size from 14.7 cm to 19.5 cm, and the serum carcinogenic antigen 19-9 level had increased from 635 U/mL to 1,918 U/mL. To prevent spontaneous rupture, laparotomy was performed, and the cyst was pathologically diagnosed as a splenic epithelial cyst.