The technique of 24-hour esophageal multichannel intraluminal impedance monitoring combined with pH-metry (MII-pH) is currently considered to be the golden standard in the diagnostics of gastroesophageal reflux disease (GERD). The technique allows for differentiation of gas and liquid reflux as well as detection of non-acid reflux, which cannot be detected with other techniques that are based only on measuring the pH of gastric contents.The aim of the study was to assess the usefulness of MII-pH in the diagnostics and treatment of GERD and its complications.Material and methods. A group of 213 patients referred to II Katedra i Klinika Chirurgii Ogólnej, Gastroenterologicznej i Nowotworów Układu Pokarmowego Uniwersytetu Medycznego w Lublinie [the Second Faculty and Clinic of General and Gastrointestinal Surgery and Gastrointestinal Oncology at Medical University of Lublin] due to persistent symptoms of GERD and 21 volunteers without any clinical evidence of GERD underwent esophageal monitoring via MII-pH. The results were correlated with those of upper gastrointestinal tract endoscopy. The data gathered during MII-pH and endoscopy as well as information from questionnaires were entered into an MS Excel spreadsheet and subsequently analyzed with STATISTICA PL software.Results and conclusions. MII-pH proved to be considerably more useful than conventional pHmetry in recording acid reflux. The sensitivity of pH-metry based on the MII-pH technique was established at 74%. GERD-induced changes in the esophageal mucosa result in decreased impedance baseline. The presence and severity of inflammatory esophageal lesions was proven to be associated with acid reflux episodes and proximal reflux episodes. No direct relationship between the grade of GERD and the occurrence of non-acid reflux episodes was confirmed. Non-acid reflux episodes were shown to predispose to non-erosive reflux disease (NERD). The results of this study confirm that MIIpH is an essential technique in the diagnostics, as well as in assessment of the course of treatment and the severity of GERD.