Extreme prematurity confers about a 100-fold increase in the risk of cerebral palsy (CP), relative to birth at term gestation. Although CP is primarily a disorder of movement, many children with this disorder have other impairments which may affect their quality of life and life expectancy. Epidemiologic and clinical studies of cerebral palsy have benefited from recent efforts to develop greater uniformity of definition and classification. Particularly noteworthy is the development of the Gross Motor Function Classification System, which is a reliable and valid measure used with increasing frequency in observational and experimental studies. Also of great importance are efforts to quantify reliably the quality of life for children with cerebral palsy, thereby providing a target for medical and community interventions that aim to increase participation and well-being among affected children. During the late 1970s and early 1980s, the rate of CP actually rose, presumably as a result of increased survival of especially vulnerable infants who otherwise would have died. In developed countries over the past two decades (late 1980s to present), CP rates have been either stable or decreasing. Although considerable effort is being directed at prevention, the only perinatal interventions for which there is strong evidence of a beneficial effect on both mortality and the risk of CP is antenatal treatment of the mother with glucocorticoid.