Relaxation of arterial and cavernous smooth muscle fibers, leading to the filling of the sinusoidal spaces with blood, are the local mechanisms of erection. Smooth muscle relaxation results from activation of parasympathetic neural pathway and probably simultaneous inhibition of the sympathetic outflow. Reflexive erection elicited by recruitment of penile afferents conveyed by the dorsal penile nerve involves both autonomic and somatic efferents. This reflex is mediated at the spinal cord level and modulated by supraspinal influences. Serotonergic pathways originating in the raphe nuclei mediate inhibitory control on reflexive erection. Several hypothalamic areas such as the medial preoptic area and the paraventricular nucleus are the source of descending pathways and/or represent important integrating centers. Dopamine acting at the medial preoptic area level may regulate penile erection. Neuroendocrine regulation may vary depending on the context in which erection occurs, for example, coitus, in response to extrinsic or psychogenic stimuli, and rapid eye movement sleep.