In order to clarify the epidemiological research on childhood motor deficiency in France there is a need to better differenciate the two terms used to define this pathology: the French term "infirmité motrice cérébrale" (IMC) and the English term "cerebral palsy" (CP). The distinction between IMC and CP is highlighted on the basis of clinical examples. IMC recovers motor deficiencies which are quite similar, however, it can be very difficult to control the variations in its use. CP has the advantage of a greater exhaustivity as well as a greater reproductibility for epidemiological records. Recently a study was conducted for measuring the prevalence of childhood deficiencies in France, and the results were expressed either as IMC or as CP. When using the CP definition the prevalence rate in France was found to be close to that of foreign studies (1.9 per thousand). In studies with etiological purposes involving several countries, a preliminary agreement on the definition of the clinical groups is absolutely necessary.