Lumbar epidural abscess and vertebral osteomyelitis were diagnosed in a 3-month-old infant, born prematurely, who had had repeated lumbar punctures for the treatment of posthemorrhagic hydrocephalus. Staphylococcus aureus was the causative organism. Successful treatment was achieved with 6 weeks of intravenous antibiotics without surgical drainage. Infectious complications of lumbar punctures are rare, but may occur when multiple punctures are attempted in small premature infants whose subarachnoid space contains large amounts of blood. Infection can be introduced directly by a contaminated spinal needle, or trauma to the tissues with bleeding can create a favorable site for bacterial adherence and multiplication. Posthemorrhagic ventricular dilation often resolves spontaneously and serial lumbar punctures should be used to treat this condition only when CSF flow is easy to establish and maintain.