A case of endosalpingiosis appearing as a huge multilocular cyst in the spleen of a 31-year-old woman is reported. The cystic lumens were smooth, and lined by fallopian tubal epithelium containing ciliated and secretory cells. The epithelial lining showed neither atypia nor foci of papillary proliferation, with only 3–5% MIB-1 labeling index. The epithelial lining was histochemically negative for mucin, but positive for MUC1 and progesterone receptor. Despite the appearance of a tumor-like mass, it was diagnosed as florid cystic endosalpingiosis as there was a normal tube-like epithelium. Regarding etiology, it was considered to derive from the secondary müllerian system of the splenic capsule.