High-resolution ultrasound has become increasingly useful in the evaluation of peripheral nerves. As we have gained experience, clinically helpful ultrasonographic signs have been detected. One of these is the ultrasonographic Tinel sign, in which paresthesias are produced when the transducer compresses a nerve lesion. This sign has not been previously described. We present a case in which the ultrasonographic Tinel sign helped accurately guide a nerve biopsy in a woman with mononeuritis multiplex.