In optical transmission systems with single channel bitrates of 10 Gbit/s and beyond the polarization mode dispersion (PMD) of the fiber may become visible as fluctuating signal distortion which may lead to high BER periods (outage). However, first concepts for PMD equalizers have already been proposed and analyzed [1,2] which adaptively track and compensate the signal distortion. In general, the PMD fluctuation driven by environmental temperature changes generates distortion fluctuation in the time scale of a few hours [3,4]. Up to now little is known about the maximum speed of PMD changes or the existence of PMD transients caused, for instance, by acoustic fiber vibration or mechanical motion. Neveflheless, even though these fast events may occur with a low probability, the speed strongly influences the design of PMD compensating units. Not only the equalizer adaptation logic need to be fast enough to track the distortion variation, but also an adequate technology for compensator components, like polarization controller or variable optical delay line, need to be chosen. In order to assess the requirements for PMD equalizers a PMD transient recorder was realized which allows to measure fast changes of PMD.