Hydrodynamic properties of hydrocephalus shunts are not always properly characterized by the manufacturer. Therefore, the choice of the shunt should be made, by matching performance of the shunt to the disturbed profile of CSF circulation of a given patient. The aim of the present shunt evaluation study is to evaluates all types of shunts presently in use in the U.K. and make this information available to neurosurgeons. Ten most common models of valves have been tested to date: Medtronik PS Medical: Delta Valve, Flow Control Valves and Lumbo-Peritoneal Shunt, Heyer-Schulte: In-line, Low Profile and Pudenz Flushing Valve, Codman: Medos-Programmable, Hakim-Precision, Sophy Programmable Valve, Cordis Orbis-Sigma. Our results show the majority of valves have low hydrodynamic resistance (exception: PS Lumboperitoneal, Orbis-Sigma), which increase by 100-200% after connection of a long distal catheter. A few shunts with siphon-preventing mechanism (Delta, Hayer-Schulte Low Profile, Pudenz-Flushing) offer reasonable resistance to negative outlet pressures, however, these valves may be blocked by raised subcutaneous pressure. All programmable valves are susceptible to siphoning. Programmed settings may be changed by external magnetic field.