The authors describe their findings in a study aimed at identifying clinical-prognostic factors in treatment of idiopathic normal-pressure hydrocephalus. The study comprised 18 adult patients submitted to surgery for ventriculo-peritoneal shunting. The findings that emerged from this series of patients were compared with those reported for the 381 published cases. In our group of 18 patients, average age was 65 years and the average duration of clinical history was 47 months (median 18 months). Follow-up ranged from 3 to 5 years (median 4.2 years): 12 patients improved (9 completely) and 6 presented stable neurological deficits. The factors that had a statistically significant influence on outcome were a short clinical history (less than 6 months) (p = 0.05) and a clinical onset without dementia (p = 0.03). Patients with medium-grade preoperative ventricular enlargement always made a complete functional recovery after surgery (p = 0.2).