Defective collagen biosynthesis in Marfan syndrome predisposes to dural defects such as dural ectasia, meningocele, and pseudomeningocele; thus, an increased index of suspicion for these conditions should be present in the clinical setting of Marfan syndrome. The authors describe a young woman with Marfan syndrome who was being treated with anticoagulants for a prosthetic heart valve and who presented with a spontaneous retroperitoneal hemorrhage requiring surgical evacuation. No CSF leak was encountered at surgery, but she developed progressively more severe positional headaches over the following year. She then experienced the sudden onset of acute urinary obstruction, at which time CT revealed a 17 × 15 × 13–cm presacral pseudomeningocele communicating with the thecal sac through a sacral bone defect. An anterior surgical approach was used for drainage of the pseudomeningocele as well as for primary closure of the dural defect with a bovine pericardial patch and autologous subcutaneous fat graft. After a short period of lumbar subarachnoid drainage of the CSF, the patient was able to resume normal activity without recurrent symptoms. To the authors' knowledge, such a pseudomeningocele in a patient with Marfan syndrome has been reported only twice, and this case features the largest pseudomeningocele to date. They also review the pertinent literature regarding presentation, diagnosis, and management of these lesions.