A 25-year-old farmer from rural Bengal presented in the emergency with acute retention of urine and severe radicular pain along the lower back and back of thighs. He had a history suggestive of bladder outflow obstruction for past 1-year, but no history of retention of urine. Radicular pain and marked constipation were of recent onset. There was no history suggestive of urinary tract infection or significant weight loss. There was no past history of surgery, trauma or other major illness. On examination, the bladder was distended and digital rectal examination revealed an anteriorly placed immobile, nontender, extra luminal soft, cystic pelvic mass. Ultrasonography revealed a cystic mass within pelvis with back pressure changes of the kidneys and ureters, while contrast enhanced computed tomography of abdomen revealed a 10.5 cm × 10 cm thick-walled, nonenhancing, unilocular lesion occupying the pouch of Douglas pressing on the bladder neck anteriorly. An ELISA test for echinococcus antigen was negative. Laparotomy revealed an immobile, retroperitoneal, tense, cystic swelling occupying the entire pelvic cavity containing crystal clear fluid suggesting possibility of hydatid cyst. Exploration of the cyst with scrupulous precautions to avoid spillage showed an endocyst. Endocystectomy with partial pericystectomy was done. Patient had an uneventful recovery. This case report depicts an atypical presentation of isolated primary extra-peritoneal pelvic hydatid cyst in a young male hailing from a nonendemic areas.