Abstract: In a population-based retrospective cohort of 5,353,022 California births from 1991 to 2000, 3,152 newborns were diagnosed with congenital hydrocephalus during the birth hospitalization. We compared demographic and clinical characteristics of infants with and without congenital hydrocephalus, and examined in-hospital fatality rates. The prevalence of congenital hydrocephalus was 5.9 per 10,000. During the study period, there was a decline in congenital hydrocephalus due to spina bifida (1.4 to 0.9 per 10,000), and an increase in congenital hydrocephalus due to obstructive hydrocephalus (0.5 to 1.0 per 10,000). Independent risk factors for congenital hydrocephalus were birth weight <1,500 g (odds ratio [OR] 51.6, 95% confidence interval [CI] 47.7-55.8) and birth weight 1,500-2,000 g (OR 14.1, 95% CI 12.4-16) compared to birth weight greater than 2,000 g, low socioeconomic status (OR 1.5, 95% CI 1.4-1.6), and male sex (OR 1.2, 95% CI 1.1-1.3). Asians had a decreased risk for congenital hydrocephalus (OR 0.7, 95% CI 0.6-0.8) when compared to whites. Thirteen percent of affected neonates died before hospital discharge.