In chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) the pathophysiology underlying permanent muscle weakness and sensory loss was studied in 22 stabilized long-term CIDP patients clinically characterized using isokinetic dynamometry, quantitative sensory testing, and neuropathy scores. Conduction velocity (CV), distal latency (DLAT), minimal F-wave latency (FLAT), compound muscle action potential (CMAP), and amplitude decay between distal and proximal stimulation sites were determined in the median, ulnar, peroneal, and tibial motor nerves and sensory CV and nerve action potentials in the median and sural nerves. Amplitude of CMAP and the DLAT were related to quantitative muscle strength, whereas CV, FLAT, amplitude decay, and dispersion were not consistently related to strength. Furthermore, CMAP and muscle strength were significantly more reduced distally than proximally. In conclusion, the electrophysiological signs of axonal loss and the associated length-dependent muscle weakness suggest secondary axonal loss in addition to primary demyelination in CIDP.