There are a number of neurological conditions that cause bladder and bowel problems in the form of neurogenic bladder and bowel dysfunction. Both have a considerable impact on a person's quality of life. Nurses have an important role to play in supporting patients when considering the options available to manage their neurogenic bladder and bowel problems. This article is the first of a series of three. Part 1 outlines the physiology of micturition and defecation. It discusses the pathophysiological changes in neurogenic bladder and bowel in spinal cord injury, spina bifida, multiple sclerosis, stroke and acquired brain injury, cerebral palsy, Parkinson's disease and diabetes mellitus. The psychosocial impact of this neurogenic dysfunction is addressed. Part 2 discusses the physical and psychosocial issues related to the management of neurogenic bowel dysfunction, and part 3 goes on to discuss the physical and psychosocial management of neurogenic bladder dysfunction.