Acute subdural hematoma (SDH) is a rare but disastrous complication after lumboperitoneal shunt placement. Four of 206 adult patients with normal pressure hydrocephalus (1.9%) who underwent lumboperitoneal shunt placement suffered acute SDH following head trauma. The interval between shunt placement and acute SDH was one month to 7 years. Two patients had subdural effusion on computed tomography (CT) at 2- and 6-month follow up. All four patients required assistance in their daily activities before acute SDH onset. The traumatic event was a fall. On admission, CT revealed a large SDH that required surgical removal in two patients, of whom one had manifested subdural effusion after shunt placement. The other two patients had a small SDH. None of the four patients had cerebral contusions. Patients with lumboperitoneal shunts, especially those not capable of independent daily activities, are at risk for acute SDH after even minor head trauma.