Neurologic diseases can affect the bowel at several levels of innervation--by altering the electrical activity that controls smooth muscle, the enteric nervous system, or the extrinsic neural pathways to the gut. This review concentrates on disorders of motility that occur in conjunction with diseases of the extrinsic neural supply (from the level of the brain to the postganglionic fibers) and those generalized disorders that affect gut smooth muscle. Modern technology, such as gastrointestinal scintigraphy and manometric techniques that measure esophageal, gastroduodenal, and anorectal motility (intraluminal pressures), has provided better methods to study the pathophysiologic aspects of gut motility in diseases of the nervous system. Distinguishing the neuropathies of the extrinsic nervous system from those of the intrinsic (enteric) nervous system is not always possible because the available techniques evaluate only the end-organ--that is, the motor function of the gut. Degenerative or infiltrative (myopathic) disorders of gut smooth muscle, however, can be distinguished from such neuropathies, and careful and systematic evaluation of autonomic function can often identify the level of disordered function in the neural-gut axis.