According to westernization of dairy life-style and aging, gastroesophageal reflux disease (GERD) with its physical symptoms such as heartburn is increasing in Japan. Although typical GERD has reflux esophagitis, GERD patients without abnormal endoscopic findings called non-erosive GERD (NERD) have been paid great attention. And more, the association between GERD and chronic respiratory diseases or laryngeal disease has been reported. To catch the more information about clinical questionnaire of GERD cases, esophageal pH monitoring is a useful method because of evaluating the direct condition of acid exposure of esophagus. Recently the new wireless pH monitoring system have been developed, this system is less stress than conventional method and has performance of pH recording for continuous 48 hours time. The widespread usage of pH monitoring system is expected to give us the new knowledge of GERD, NERD and GERD associated diseases.