The cerebellar vermis has been recognized as a key region of a circuit essential for long-term habituation of the acoustic startle response in rats. The removal of this neuronal structure before training prevents the build-up of this long-term behavioral change. Our data show that, when the same lesion is performed after training for long-term habituation, the learned behavior is not affected. These results indicate that the cerebellar vermis is essential for the acquisition, but not for the retention of long-term habituation of the startle response.