Three cases of hypertrophic interstitial neuropathy with severe decrease of motor nerve conduction velocity are reported; on sural nerve biopsy was found the typical onion bulb formation, with connective tissue proliferation. The pathogenesis of the onion bulb formation and the correlation with the decreased motor nerve conduction are discussed. The authors concluded that only one of the cases could be named Dejerine-Sottas disease, since the others probably are Charcot-Marie-Tooth disease cases.