We report on a 27-year-old Caucasian female with congenital cataract and mental retardation complaining of progressive paresis and atrophy of the lower legs beginning at the age of 16 years followed by atrophy of the thighs and small hand muscles. Motor and sensory conduction velocities (CV) of the upper and lower limbs were reduced (distal peroneal nerve: 21 m/s; median nerve: motor CV: 28 m/s, sensory CV 30 m/s). In the sural nerve biopsy specimens there were unique endoneurial cells immunoreactive for antibodies against the epithelial membrane antigen with multiple surface indentations and projections considered to be dysplastic perineurial cells. To the best of our knowledge these cells have not been reported in any other type of human peripheral neuropathy. The present case with the above clinical and structural findings appears to represent a new, complex, demyelinating type of a sporadic or possibly recessively inherited motor and sensory neuropathy.