BACKGROUND: Cerebral palsy (CP) is the most common childhood motor disability. The emergence of genetic CP etiologies, variable inclusion of hypotonic CP in international registries, and involvement of different medical disciplines in CP diagnosis can promote diagnostic variability. This variability could adversely affect patients' understanding of their symptoms and access to care. Therefore, we sought to determine the presence and extent of practice variability in CP diagnosis. METHODS: We surveyed physicians in the United States and Canada interested in CP on the basis of membership in the American Academy of Cerebral Palsy and Developmental Medicine or the Child Neurology Society Neonatal Neurology, Movement Disorders, or Neurodevelopmental Disabilities Special Interest Groups. The survey included the 2007 consensus definition of CP and 4 hypothetical case scenarios. RESULTS: Of 695 contacted physicians, 330 (47%) completed the survey. Two scenarios yielded consensus: (1) nonprogressive spastic diplegia after premature birth with periventricular leukomalacia on brain MRI (96% would diagnose CP) and (2) progressive spastic diplegia (92% would not diagnose CP). Scenarios featuring genetic etiologies or hypotonia as the cause of nonprogressive motor disability yielded variability: only 46% to 67% of practitioners would diagnose CP in these settings. CONCLUSIONS: There is practice variability in whether a child with a nonprogressive motor disability due to a genetic etiology or generalized hypotonia will be diagnosed with CP. This variability occurred despite anchoring questions with the 2007 consensus definition of CP. On the basis of these results, we have suggested ways to reduce diagnostic variability, including clarification of the consensus definition.