An adult male with C-7 quadriplegia developed neck pain. Axillary F central latencies were prolonged, and MRI showed a syrinx extending to C-1. After shunting, F latencies normalized. At subsequent follow-up, a rostral syrinx persisted by magnetic resonance imaging (MRI); motor evoked potential (MEP) latencies were prolonged but F latencies were normal. Later, the syrinx was less distended by MRI, MEPs normalized, and strength improved. We discuss the electrophysiologic methods available for diagnosing and monitoring posttraumatic syringomyelia.