Natural history of idiopathic normal-pressure hydrocephalus (INPH) is not clear. We performed a literature search for studies that looked into the outcome of unshunted INPH patients trying to answer the following questions: Do all INPH patients deteriorate without shunt? If yes, at what rate? Do some NPH patients improve without shunt? If yes, to what extent? Six studies objectively described the outcome of 102 INPH patients. Result shows that without surgery, most INPH patients had measurable deterioration as early as 3 months following initial assessment. A small number of patients might improve without shunt, however the extent of improvement is not clear. The homogeneity of the findings of the cohort studies provided high evidence supporting the rule of shunt surgery in INPH patients.