A 35 year old woman presented with two episodes of spastic paraparesis, occurring in the third trimester of two consecutive pregnancies. The neurological symptoms seemed to be caused by an intramedullary cyst in the thoracic spinal cord. The cyst was subtotally removed and histopathologically diagnosed as enterogenous cyst. Other congenital abnormalities were absent. The peculiar timing of the clinical manifestation of an intramedullary cyst has not been described before. An unequivocal explanation for this phenomenon is missing, but several factors related to pregnancy that may play a part are discussed.