We report on the clinical, electrophysiological, and lower-limb musculature MRI findings in a severe demyelinating Guillain-Barré syndrome (GBS) patient with follow-up over 6 months. After 3 weeks of tetraplegia and mechanical ventilation, there was progressive improvement until almost complete recovery. On day 4 after onset, electrophysiological study revealed absent F waves and widespread conduction block. On four further electrophysiological studies on days 12, 19, 45, and 150, there was marked and reversible slow down of motor conduction velocities in upper-limb nerves, and persistent inexcitability of lower-limb nerves. Mild signs of active denervation were recorded in calf and foot muscles as of day 45. On day 39, MRI T2-weighted fat-suppressed images showed patchy hypersignal of variable intensity involving pelvic, thigh, and calf muscles, which disappeared in a second imaging study on day 190; in this study T1-weighted images did not disclose muscle fatty atrophy. We conclude that in severe demyelinating GBS prolonged motor nerve inexcitability should not necessarily be taken as a predictor of poor prognosis, and that MRI is useful in assessing the topography and evolution of muscle denervation.