We used a binomial regression model to determine the relationship between the percent of cerebrospinal fluid (CSF) mononuclear white blood cells and symptom duration in children with proven enteroviral meningitis. The odds of a CSF white blood cell being mononuclear increased by 15.7% (95% confidence interval: -3.8% to 38.0%; P = .11) for each day of symptoms. Fifty percent of patients with symptoms of 1 day or less had predominance of mononuclear cells among CSF white blood cells. These findings suggest that factors other than symptom duration influence the composition and evolution of the CSF white blood cell response to enteroviral infection.