Gastroesophageal reflux is a very common disorder. Typical symptoms are heartburn, regurgitation and chest-pain. Recently, it has been demonstrated that gastroesophageal reflux may generate or worse extraesophageal symptoms such as asthma, chronic bronchitis, posterior laryngitis, and chronic cough. The diagnosis of gastroesophageal reflux is suggested by typical symptoms which improve under a therapy with proton pump inhibitors, pH-monitoring over 24 hours is able to establish directly the diagnosis by measuring acid reflux into the esophagus. Manometry detects the two most common causes of gastroesophageal reflux: insufficiency of the lower esophageal sphincter or esophageal motility abnormalities. Gastroesophageal reflux can lead to reflux esophagitis, which is diagnosed endoscopically. An endoscopy should routinely be performed in case of dysphagia, anemia, or loss of weight. A long-term sequela of,gastroesophageal reflux is the development of Barrett's-esophagus, a condition which has to be verified by endoscopy and biopsy. This premalignant lesion is defined by a metaplastic change from the normal squamous mucosa to a specialized intestinal epithelium characterized by globlet cells. Because dysplasia in these metaplastic areas can lead to esophageal adenocarcinoma, regular endoscopic surveillance with biopsies is recommended. Gastroesophageal reflux can significantly impair the quality of life and can cause complications that include the neoplastic progression from Barrett's esophagus to carcinoma. Therefore, appropriate diagnostic procedures and adequate therapy are required. This article summarizes the diagnostic approach to patients with gastroesophageal reflux, reflux esophagitis and Barrett's-esophagus. The impact of endoscopy, pH-monitoring, esophageal manometry, radiology and szintigraphy are reviewed.