The International Workshop on the Definition and Classification of Cerebral Palsy have proposed a fresh definition and classification of cerebral palsy (CP; p 571). In their accompanying paper they explain their reasoning behind this. Why is there the need for revision of the widely accepted and comfortably familiar definitions of Bax and Mutch? These definitions are beautifully succinct and clear but perhaps not inclusive enough, making no mention of pathogenesis or of the functional and ‘non-motor’ features of CP which are most significant when it comes to everyday life. There has been debate in the past as to whether a more aetiological definition should be adopted but we are not yet ready for this. CP remains unexplained in around 15% of children, even after good neuroimaging and metabolic investigation and we recognize that a wide range of CNS disorders can result in a similar clinical picture. Thus, a predominantly phenotypic definition and classification remains the most appropriate. The workshop clearly deliberated long and hard over every word of the revised definition producing a much more detailed description of CP that now encompasses the effect on function (activity limitation) and the comorbid features. As a result, the definition is longer and it does not ‘trip off the tongue’ in the way the old ones did.