The pathology of the peripheral nervous system (PNS) in 2 autopsied cases of group A xeroderma pigmentosum (De Sanctis Cacchione syndrome) are presented. Motor nerves including those of the oculomotor systems were severely affected, but involvement of the sensory system was even more marked. Minor hypertrophic changes were present in the distal portions of the peripheral nerve trunks, but there was no appreciable difference in the density of myelinated nerve fibres between proximal and distal levels. Morphometric data including teased fibre analyses and g ratio scattergrams suggest that the underlying pathogenetic mechanism is that of a neuronopathy. Unmyelinated axons were also severely depleted. Review of the previous literature revealed that the pathological changes of the PNS in group A xeroderma pigmentosum are thought to be slowly progressive, which is also suggested by the severe and widespread sclerotic changes of the CNS in the present 2 cases.