Introduction: Malfunction of cerebrospinal shunts is common and due to multiple etiologies. We hypothesize that opening of the spinal dura may prompt shunt failure in select individuals with previously unrecognized tenuous shunt function. Case reports: The authors describe five patients with shunted hydrocephalus who underwent procedures in which the spinal dura mater was opened. All patients had acute dysfunction of their ventriculoperitoneal shunt that required shunt revision. All shunt valves were functioning properly at operative inspection but all patients were found to have adherent intracranial catheters with ingrowth of choroid plexus. Conclusions: We theorize that the siphoning effect caused from cerebrospinal fluid egress from the opened spinal subarachnoid space resulted in acute shunt failure. Such alterations in cerebrospinal fluid flow may precipitate complete failure of a shunt that is functioning suboptimally. Clinicians should be aware that spinal procedures that violate the subarachnoid space in shunted hydrocephalic patients may result in acute shunt failure. These patients may warrant more careful observation in the early postoperative period, particularly as shunt failure may compromise spinal wound closures. © 2009 Springer-Verlag.