We studied the neuropsychological function including mental status and motor development, and cellular susceptibility to UV killing in four Cockayne syndrome (CS), of whom three were classic form (type I) and one was congenital form (type II). The results showed that there was no correlation between the age at symptomatic onset of CS neurological disorders and the levels of cellular UV-hypersensitivity and that neuropsychological impairment did not parallel cellular hypersensitivity to UV killing. It was suggested that the cellular UV-hypersensitivity might not be the essential cause of neurodegeneration in CS.