Adult-onset hypothyroidism is associated with an increase in cell atrophy of the hippocampal pyramidal neurons. Physical exercise implies diverse actions on the neural tissue that promote neuron proliferation and survival. The beneficial effects of exercise seem to be inversely linked to its intensity, so that strenuous exercise has reduced protective effects. In this study we evaluated the capacity of a moderate forced-exercise routine to counteract the neurodegenerative effects of a hypothyroid condition induced during adulthood. Simultaneously with a chronic anti-thyroid chemical treatment, a group of rats was forced to walk in a motorized wheel for 30 min daily five times a week. In four weeks of treatment the rats developed a plain hypothyroid condition that in non-exercised rats was accompanied by a marked increase in the number of atrophic cells in all CA regions of the hippocampus. The forced-exercise treatment did not counter the development of hypothyroidism and its signs, but it did prevent almost completely the associated neuronal damage in all CA regions. The forced exercise also improved the cognitive function in a spatial-learning test. These results indicate that moderate exercise has the potential to prevent the structural and functional deficits associated with a hypothyroid condition.