We describe a 14-year-old girl with Marfan syndrome who presented with severe postural headache. Dural ectasia was demonstrated radiologically. Cerebrospinal fluid (CSF) pressure was immeasurable on formal measurement. Radionucleide cisternography failed to demonstrate a CSF leak. We consider that the underlying fibrillinopathy in Marfan syndrome rendered the dura sufficiently permeable to CSF leakage to cause the low CSF pressure headache. The patient was treated successfully with epidural autologous blood patch.