An out-patient follow-up study of 41 patients suffering from cryptogenetic PNP was performed: 19 (46%) had a symmetric-paretic; 15 (37%) a symmetric-sensory, 4 (10%) an asymmetric type polyneuropathy and 3 (7%) presented with mononeuropathia multiplex; 12 of 41 (29%) unclassified PNP could be clarified. Of the remaining 29 unsolved cases, 14 (48%) formed a homogeneous subgroup sharing specific criteria: primary, axonal type degeneration; slowly progressing clinical course reaching a plateau; low disability status; onset between the age of 45-65. We concluded that out-patient re-evaluation of cryptogenetic PNP yields improved diagnosis. Hereditary and immune-mediated PNP exhibit specific diagnostic problems and account for a large portion of the cryptogenetic PNP.