This study was aimed to investigate neuropathological changes in adult and aged rats subjected to supplementary iron administration in a critical postnatal period to study the contribution of environmental risk factors to the pathogenesis of neurodegenerative disorders. Ten rats received a single daily oral administration of iron (10 mg/kg) between 12th and 14th post-natal days; nine rats received vehicle (sorbitol 5% in water) in the same period. Five iron-treated and three sorbitol-treated rats were killed at the age of 3 months while five iron-treated and six sorbitol-treated rats were killed at age of 24 months and their brains processed for immunohistochemistry. Increased astrocytosis, revealed by densitometry of GFAP-immunoreactive astrocytes, was found in aged (24 months) iron-treated rats in the substantia nigra and striatum and in the hippocampus of adult (3 months) iron-treated rats when compared to age-matching controls. Decreased densitometry of neurons, revealed by neuronal nucleus immunohistochemistry, was found in aged (24 months) iron-treated rats in substantia nigra and striatum when compared to age-matching controls. These findings suggest that transient dietary iron supplementation during the neonatal period is associated to cellular imprinting in the brain later in life.