This study carried out clinical, electrophysiological and morphological investigations (sural nerve and gastrocnemius muscle biopsies) in a group of 47 patients with neuromuscular disease of a certain or supposed degenerative origin and a late onset (over the age of 30 yrs.). It aimed the evidence of the eventual particularities of such diseases with a delayed onset. The equal involvement of sexes, the insidious onset, the clinical picture similar to that of the corresponding diseases with an onset at the usual age were observed. Regardless of the age, some interesting associations of the polyneuropathy with other diseases or its presence with in these diseases (Parkinsonism, Addison's disease, multiple symmetrical lipomatosis, etc.) were noticed, too. Electrophysiological examinations showed no particularities. Neither did the muscular morphological picture in most of the cases presenting neurogenic lesions with a moderate intensity. The sural nerve biopsy evidenced in 70% of the cases a moderately intense neuropathy of an axonal type ("dying back"), with or without secondary lesions of segmental demyelination and with the signs of a live regenerative activity.