OBJECTIVE: Chorioamnionitis is associated with increased risk for cerebral palsy (CP) in term infants. A functional polymorphism in the interleukin-6 (IL-6) gene has been implicated in newborn brain injury. We studied whether the IL-6 -174 G/C polymorphism confers increased risk for CP in term infants. METHODS: This population-based case-control study included 334,333 live-born infants born at >or=36 weeks gestation within Kaiser Permanente Medical Care Program from 1991 to 2002. Case patients (n = 250) were identified from electronic records and confirmed by chart review, and comprised all infants with spastic or dyskinetic CP not caused by developmental abnormalities who had a neonatal blood specimen available for study. Control patients (n = 305) were randomly selected from the study population. RESULTS: Compared with genotype GG, the less common CC genotype was associated with increased risk for overall CP (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.5-4.6), quadriparetic CP (OR, 4.1; 95% CI, 1.8-9.3), and hemiparetic CP (OR, 2.7; 95% CI, 1.3-5.7), after controlling for race. The C allele conferred increased risk for CP in both recessive and additive genetic models. In multivariate analysis controlling for race, independent risk factors for CP included CC genotype compared with GG (OR, 2.4; 95% CI, 1.3-4.4), clinical chorioamnionitis (OR, 4.6; 95% CI, 2.1-10.4), maternal age >or= 35 (OR, 2.6; 95% CI, 1.6-4.1), and male sex (OR, 1.6; 95% CI, 1.1-2.4). INTERPRETATION: Our data suggest that a functional polymorphism in the IL-6 gene is a risk factor for CP among term and near-term infants.