The subthalamic nucleus (STN) has been regarded as an important modulator of basal ganglia output. It receives its major afferents from the cerebral cortex, thalamus, globus pallidus externus and brainstem, and projects mainly to both segments of the globus pallidus, substantia nigra, striatum and brainstem. The STN is essentially composed of projection glutamatergic neurons. Lesions of the STN induce choreiform abnormal movements and ballism on the contralateral side of the body. In animal models of Parkinson’s disease this nucleus may be dysfunctional and neurons may fire in oscillatory patterns that can be closely related to tremor. Both STN lesions and high frequency stimulation ameliorate the major motor symptoms of parkinsonism in humans and animal models of Parkinson’s disease and reverse certain electrophysiological and metabolic consequences of dopamine depletion. These new findings have led to a renewed interest in the STN. The aim of the present article is to review briefly the major anatomical, pharmacological and physiological aspects of the STN, as well as its involvement in the pathophysiology and treatment of Parkinson’s disease.