Cypermethrin is a Type II pyrethroid widely used for pests control in agriculture. The principal effect of this insecticide is to alter voltage-dependent sodium channels in the nervous system, but it also affects GABA levels in the CNS of mammals. The cerebellar circuit has as its principal neurotransmitter GABA for transportation of Cl-, allowing its inhibitory and modulatory function. In this work, the effects of cypermethrin on the cerebellar cortex are studied. Thirty three adult CF-1 male mice were distributed in three groups: 1) untreated, 2) vehicle (oil) and 3) experimental (cypermethrin in oil at 1/5 DL50). The animals were euthanized at days 1, 8, 17, 25 and 34; then processed for histology (haematoxylin-eosine) and im munohistochemistry (Apaf-1 and Ki-67). The Purkinje cells and the immunoreactive Purkinje and Granular cells were quantified. The results showed a significant decrease in Purkinje cells numbers at all the times studied; also, there was an increase in the expression of Apaf-1 and Ki-67 in the Purkinje and Granulizr cells in acute and chronic stages. This shows that cypermethrin at 1/5 DL50 produces damage to the cerebellar cortex and induces apoptosis in the Purkinje and Granular cells.