['Combined 24-h multichannel intralumenal impedance-pH monitoring (MII-pH) is gaining popularity as a diagnostic tool for gastroesophageal reflux. Since the surgical reduction of hiatal hernias and creation of a fundoplication anatomically restores the gastroesophageal reflux barrier, one would assume that it effectively stops all reflux regardless of composition. Our aim is to evaluate the results of routine MII-pH testing in successful Nissen fundoplication patients.', 'Sixty-two patients with normal acid exposure, confirmed by 24-h pH testing, after Nissen fundoplication were evaluated with symptomatic questionnaire, esophageal manometry and MII-pH testing more than 6 months after surgery. Patients were grouped into normal and abnormal based on postoperative impedance results. Patients with Nissen alone were separately compared to patients with Nissen + giant hiatal hernia (GHH).', 'Twenty-nine (47%) patients exhibited abnormal impedance after successful Nissen fundoplication. Abnormal impedance was associated with GHH repair, lower bolus pressures, and lower distal esophageal contraction amplitudes.'] Is postoperative impedance-pH testing unreliable after Nissen fundoplication with or without giant hiatal hernia repair?