Mesenteric cysts are rare intra-abdominal masses, presenting with various clinical signs and symptoms. Mesenteric cysts presenting with a sudden onset of urinary retention is extremely rare. There are no cases reported in the English literature. Here, we report a very rare case of urinary retention, due to mesenteric cyst in a 19-year-old man. The patient presented with abdominal distention with a sudden onset of urinary retention. Ultrasonography and computed tomography scan of the abdomen revealed a huge cystic mass above the bladder that was completely separated from the kidney and bladder. The cyst was removed surgically. The patient experienced no urological difficulty after the surgery. Histological examination confirmed the diagnosis of a mesenteric cyst.