Cerebrospinal fluid (CSF) penetration of imipenem-cilastatin was evaluated in 20 children (aged 4 months to 11 years) with central nervous system infections. A total of 10 children received a single 25-mg/kg intravenous dose, and 10 received three 25-mg/kg intravenous doses at 6-h intervals. Blood and CSF were obtained 1.5 to 2.5 h after the last dose during the early (days 1 to 3) and the late (days 7 to 10) stages of infection. Imipenem concentrations after single-dose infusion in serum and CSF during the early phase of treatment (8.59 +/- 0.95 and 1.36 +/- 0.32 micrograms/ml, respectively) were similar to those during the late phase (9.96 +/- 2.36 and 2.08 +/- 1.14 micrograms/ml, respectively). Concentrations of imipenem in serum and CSF after multiple-dose infusion during the early phase (11.97 +/- 2.03 and 1.87 +/- 0.29 micrograms/ml, respectively) were similar to those during the late phase (9.57 +/- 1.76 and 1.22 +/- 0.11 micrograms/ml, respectively). There were no significant differences in the serum or CSF imipenem concentrations between the single- and multiple-dose groups during the early or late treatment stages. Cilastatin concentrations in serum and CSF were similar in all groups with the exception of the multiple-dose, early- versus late-phase evaluation of CSF cilastatin concentration. There was no correlation between age or absolute CSF neutrophil count and the serum or CSF concentrations of imipenem or cilastatin. We found a mean CSF penetration of 15 to 27% for imipenem and 16 to 66% for cilastatin in children. These findings suggest that imipenem-cilastatin sufficiently penetrates into CSF in children to warrant further investigation of this compound in pediatric central nervous system infections.