The cerebrospinal fluid tap test (CSFTT) is recommended as a key step in the diagnosis of idiopathic normal pressure hydrocephalus (iNPH). While there is no generally accepted evaluation period for ascertaining a CSFTT responder, a substantial number of patients are evaluated only once within 24 hours of the test for improvement in gait. We report an iNPH patient with a favorable response to shunt surgery, who was first judged a non-responder by this standard, though subsequently was judged a responder in virtue of repetitively testing gait over 7 days. A 68-year-old man presented with progressive impairment of gait, balance, and memory. He was diagnosed as iNPH with an Evans' ratio of 0.35. At first hospitalization, change in gait was evaluated 24 hours after the CSFTT. He didn't show any significant improvement and was judged as a non-responder. However, at the second CSFTT, we repetitively tested his change in gait over seven days. Forty-eight hours after the tap, he showed significant improvement in his gait. He was then confirmed as a responder. After the operation, the gait difficulties were almost fully resolved. Further studies developing the standard procedure of the CSFTT should be considered.