Anterior sacral meningocele has been reported to be associated with Marfan syndrome (MFS) in few cases, differently from dural ectasia appearing up to two thirds of affected patients. A new instance of this association is described in an 18-year-old man with Marfan syndrome, diagnosed upon MRI morphological evaluation which showed a huge cystic mass in the pelvic space. Surgical excision even if curative was not performed in consideration of a stationary picture after one year since diagnosis.