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Secondary normal pressure hydrocephalus (NPH) frequently occurs after severe head injury and cerebrovascular disease. This condition is usually treated by surgically implanting a cerebrospinal fluid (CSF) shunt with a pressure-setting valve or programmable valve. However, some patients do not respond to the shunt operation. Among these non-responders, we found 7 patients whose pressure-setting shunts were mechanically patent, but were not functioning due to very low intracranial pressure (ICP). In these 7 cases, continuous ICP monitoring indicated low pressure with occasional negative pressure, and the patients' consciousness improved during negative-pressure CSF drainage. We performed shunt revisions with zero setting on-off valves, which raised the mean functional independence measure (FIM) scores from 26 to 62. Four patients in a persistent vegetative state (PVS) regained their ability to communicate and recovered to the level of severely disabled (SD). We propose very low-pressure hydrocephalus (VLPH) as a new clinical entity, and describe the process of diagnosis and treatment.