In 1977, Fisher reported that in patients with possible normal-pressure hydrocephalus (NPH), if the gait abnormality preceded dementia, surgery usually had a favorable outcome and vice versa. We studied this finding in 21 patients shunted for possible NPH. By evaluating serial videotapes of gait, neuropsychological tests, and Katz index ratings, preoperatively and at approximately two months and six months postoperatively, we judged 16 patients improved. In the improved group, the families reported that the gait abnormality preceded the dementia in 11 patients and occurred at the same time in five. In the unimproved group, dementia was noted first in three patients, gait abnormality first in one patient, and gait abnormality and dementia at the same time in one patient. Using Fisher's exact test, we compared the improved and unimproved groups for gait abnormality or dementia onset first and found a significant difference. We conclude that the history of gait abnormality occurring before or after dementia in patients with possible NPH is an important prognostic factor for surgical outcome.