Neonates with posthemorrhagic hydrocephalus require close follow-up, and may require lumbar punctures, acetozolamide, ventricular drainage, or ventriculoperitoneal shunt. Close follow-up consists of daily head circumference measurements and assessment of fontanelle tension and interparietal suture distance. Lumbar puncture should be performed at the L2-L3 or L3-L4 intervertebral space. The neck of the neonate should not be flexed. The amount of fluid to be extracted should be 10 to 15 cc/kg. The cerebrospinal fluid should be studied for cell count, glucose, protein, and bacterial cultures. The success of a lumbar puncture is judged by the amount of cerebrospinal fluid removed and the comparison of the fontanelle tension and ventricular size by brain ultrasound before and after the lumbar puncture. A lumbar puncture is considered successful if the fluid removed is 10 cc/kg or more, and if the fontanelle tension and ventricular size decrease after the procedure. Acetozolamide decreases the production of cerebrospinal fluid. The dose is 100 mg/kg per day in 2 doses. Ventricular drainage may be performed by multiple ventricular taps or by placing a continuous reservoir. Ventriculoperitoneal shunt is the treatment of choice for nonarrested hydrocephalus. Ventriculoperitoneal shunt should be performed when the neonate weighs over 1500 grams, the cerebrospinal fluid has less than 1000 red cells per cubic centimeter, the protein concentration is less than 500 mg/dL, and the patient is clinically stable. A CT of the brain prior to placement of the ventroperitoneal shunt is recommended.