Schwannomas are peripheral nerve sheath tumours with a slow growth rate. Giant sacral schwannoma with anterior cortex erosion and associated intrapelvic extension are uncommon. Though they tend to be large when initially found, most Giant schwannomas are clinically asymptomatic. The tumour appears heterogenous due to long standing degeneration. Herein, we present a case of a large purely cystic presacral schwannoma in a patient with poliomyelitis, which has displaced adjacent organs including urinary bladder and sigmoid colon, with an initial presentation of constipation. The tumour was partially excised and diagnosis was confirmed by histo-pathology and immunohistochemistry.