For a variety of reasons, the definition and the classification of cerebral palsy (CP) need to be reconsidered. Modern brain imaging techniques have shed new light on the nature of the underlying brain injury and studies on the neurobiology of and pathology associated with brain development have further explored etiologic mechanisms. It is now recognized that assessing the extent of activity restriction is part of CP evaluation and that people without activity restriction should not be included in the CP rubric. Also, previous definitions have not given sufficient prominence to the non-motor neurodevelopmental disabilities of performance and behaviour that commonly accompany CP, nor to the progression of musculoskeletal difficulties that often occurs with advancing age. In order to explore this information, pertinent material was reviewed on July 11-13, 2004 at an international workshop in Bethesda, MD (USA) organized by an Executive Committee and participated in by selected leaders in the preclinical and clinical sciences. At the workshop, it was agreed that the concept 'cerebral palsy' should be retained. Suggestions were made about the content of a revised definition and classification of CP that would meet the needs of clinicians, investigators, health officials, families and the public and would provide a common language for improved communication. Panels organized by the Executive Committee used this information and additional comments from the international community to generate a report on the Definition and Classification of Cerebral Palsy, April 2006. The Executive Committee presents this report with the intent of providing a common conceptualization of CP for use by a broad international audience.