The effects of long-term treatment (11 months) with acetyl-L-carnitine (75 mg/kg daily) on the morphology of brain and optic nerve was studied in 16 senescent (22-month-old) Wistar rats (nine untreated, seven treated). Five young rats (aged 3 months) were used for comparison. Senescence was found to cause a structural disorganization of cerebral cortex, hippocampus and cerebellar cortex, and a decrease in the volume densities of the pyramidal neurons of layers 2 and 5 of the prefrontal cortex. An impaired myelination of the pyramidal tract and of the optic nerve was also observed. Besides improving the structural organization of the cerebral areas under study, treatment with acetyl-L-carnitine increased the volume densities of pyramidal neurons of the prefrontal cortex layers under observation. It must be added that myelination of the pyramidal tract and optic nerve was found to be less impaired after acetyl-L-carnitine administration.