The rapid increase in the number of cell phone users has led to the suggestion that electromagnetic waves might affect medical devices. Cerebrospinal fluid shunt valves contain a magnetic device to allow the intracranial pressure setting to be adjusted transcutaneously. Among the valves tested, the settings of the Strata valve, the Hakim valve, and the Sophy valve were affected by magnetic flux densities of 6.0, 17.5, and, 40.0 mT, respectively. Cell phones produce a magnetic flux density of 3.0 to 40.0 mT. Although cell phones could theoretically influence shunt valves, this seems unlikely because the flux density decreases with the square of the distance.