A case of retroperitoneal cystic lymphangioma in which cystic fluid analysis using endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) was helpful for diagnosis is reported. A 40-year-old man was referred and admitted to our department for further examination with a chief complaint of back pain, and detailed examination revealed a pancreatic cyst. Abdominal contrast-enhanced CT showed a non-enhancing, lobulated, cystic lesion surrounded by the pancreatic tail, spleen, left kidney, and stomach. Magnetic resonance cholangiopancreatography showed a multilocular cyst but no dilation of the main pancreatic duct. On duodenoscopy, no mucus excretion was observed. Pancreatography showed no translucency indicative of mucus, and the cyst was not visualized even after increasing the contrast pressure. Endoscopic ultrasound showed a multilocular cystic lesion in the pancreatic tail that was 80 mm in diameter and consisted of loculi of various sizes. No nodes were seen. Intraductal papillary mucinous neoplasm was ruled out based on the above imaging findings, and EUS-FNA was performed on the cyst for differential diagnosis between serous cystic neoplasms and pancreatic pseudocysts. The cystic fluid was yellowish, and based on the findings that CEA was within the normal range and amylase was only slightly elevated (161 IU/l), mucinous tumor and pancreatic pseudocyst were ruled out. Because the patient remained symptomatic, the cyst was removed surgically. Histopathological analysis showed that the tumor consisted of cysts of various sizes. The cyst wall was composed of a single squamous epithelial layer with no atypical cells, and smooth muscle components were also observed. The patient was diagnosed as having cystic lymphangioma.