Twenty-seven newborn infants (birth weight, 1503 +/- 776 g; gestational age, 31 +/- 3 wk) (mean +/- standard deviation) with rapidly progressive posthemorrhagic hydrocephalus and increased intracranial pressure were treated by external ventricular drainage. The progression of hydrocephalus was arrested during the drainage period in each patient. The drainage was kept in place for 23 +/- 9 days, the longest drainage period being 48 days. In 16 of 23 surviving patients, progressive ventricular dilation recurred after removal of the drainage, requiring a definitive shunt implantation (nine ventriculoatrial, seven ventriculoperitoneal). For the remaining seven infants, no further therapy was necessary. Implantation of the permanent shunt was done days 28 to 88 (body weight, 2400 +/- 950 g). Bacterial cultures from cerebrospinal fluid and/or the tip of the ventriculostomy catheter were negative in 175 instances and positive in 11 instances (7 patients). No clinical or biochemical evidence of ventriculitis was noted. Four of the 27 patients died of causes unrelated to external ventricular drainage. Twenty-three infants survived. Seventeen of 23 survivors suffered from intraventricular hemorrhage Grade 3; in 7, neurological and developmental outcomes were classified as normal; 9 patients experienced mild to moderate paresis and/or mild to moderate developmental delay; and only 1 patient was severely retarded. Six patients with parenchymal lesions had severe motor and/or developmental handicaps. We consider external ventricular drainage an effective and safe therapy in newborn infants with rapidly progressive posthemorrhagic hydrocephalus and increased intracranial pressure. The ultimate outcome, however, depends mainly on the mode and the extent of the primary brain lesion.