['To determine if the association of cerebral palsy (CP) with umbilical cord around the fetal neck (nuchal cord) is the result of recording bias.', 'Population-based case control study.', 'There were 68 cases with cerebral palsy and 157 controls (singleton term infants matched for gestational age and hospital of birth). CP was associated with tight nuchal cord overall (OR=2.8, 95% CI 1.1-6.8). Where cord around the neck is recorded at the discretion of the accoucheur (37 cases, 97 controls), there was an association between tight nuchal cord and CP (OR=5.4, 95% CI 1.4-20.4) and, in controls only, between Apgar score <7 at 1 min (OR=16.9, 95% CI 1.4-456.3). In the hospital where records included a tick box for nuchal cord (31 cases, 60 controls), an association between CP and tight nuchal cord could not be demonstrated (OR=1.4, 95% CI 0.4-4.9). Nor was there an apparent association between nuchal cord and Apgar score <7 at 1 min (OR=2.6, 95% CI 0.4-15.9) in controls.'] Is the association of nuchal cord with cerebral palsy influenced by recording bias?