This observation relates a case of spinal arachnoiditis with paraplegia, for a 56 year old patient hospitalized for a S.A.H. by a ruptured aneurysm of the P.I.C.A. This patient present some complications, requiring a prolonged ventilatory support with a tracheostomy, a ventricular shunt for hydrocephalus. The treatment is only surgical, and the corticosteroids delay the evolution, but without successful outcome.