This study was designed to assess the feasibility of intrathecal gadolinium-enhanced magnetic resonance cisternography (MRC) for the evaluation of the presence or absence of communication of cranial arachnoid cysts with the cerebrospinal fluid (CSF) pathways of the central nervous system (CNS). This prospective study included 20 patients (12 males and 8 females) with a mean age of 37 years, who had, as a group, 22 intracranial arachnoid cysts identified on prior CT and/or MR examinations. Routine pre-contrast cranial MR imaging was followed by the intrathecal administration of 0.5 cc gadopentetate dimeglumine (GD) (Magnevist, Schering, Germany). Immediate and delayed (24 h) MR cisternography was then carried out. Eleven of 22 arachnoid cysts showed immediate CSF communication by the demonstration GD-contrast enhancement of the cyst fluid on the immediate post-injection scan. Contrast enhancement of the cyst was observed only on delayed MRC in six patients. MR imaging in five patients demonstrated no contrast enhancement of the arachnoid cysts on either immediate or delayed imaging. Six patients had mild transient post-procedure headache that was relieved by oral analgesics within 24 h. No serious immediate or chronic adverse effects or complications relating to the intrathecal contrast administration were observed. This study showed the relative safety, feasibility and reliability of low-dose intrathecal GD MR imaging in the demonstration of the communication or non-communication of intracranial arachnoid cysts with the CSF pathways of the CNS. In the future, this may have bearing on the selection for surgery of patients with intracranial arachnoid cysts presenting with clinical signs and symptoms potentially related to the location and mass effect of the cyst. © Springer-Verlag 2004.