For diagnosis and quantitation of gastroesophageal reflux disease, a number of different examinations are available. The simplest are the patient's history and complaints as well as the proton pump inhibitor test; both methods have a positive predictive value of 65% to 70%. Esophagogastroduodenoscopy is the gold standard for differentiation between erosive and nonerosive reflux disease. Biopsy does not enhance the significance of endoscopy except for proof of Barrett's epithelium or malignant degeneration. Twenty-four-hour pH monitoring has the highest sensitivity and specificity for the diagnosis of gastroesophageal reflux disease. Barium swallow provides only additional information concerning hiatal hernia or stenosis. Manometry can clarify lower esophageal sphincter insufficiency or motility disorders of the tubular esophagus. However, the available studies show that manometry has no influence on postoperative outcome after fundoplication. The indication for medical therapy can primarily be based only on the history and complaints of the patient. As surgical therapy affords a high degree of diagnostic accuracy, at least endoscopy and 24-h pH monitoring are necessary for indication.