This study is a phase III, multi-centre, randomized, double-blind study to assess the safety and tolerability of once daily treatment with esomeprazole 20 or 40 mg in pediatric and adolescent patients 12 to 17 years of age, inclusive, with clinically diagnosed GERD. The treatment period will be up to 8 weeks.

Inclusion Criteria:

• Provision of signed written informed consent from the patient's parent/guardian, and assent from the patient prior to conducting of any study-related procedures.
• Patients must be male or female between the age of 12 and 17 years, inclusive.
• Patients must have a clinical diagnosis of GERD made by the investigator based on any of the following factors: history, physical examination, review of systems, laboratory test results, or information from diagnostic testing.

Exclusion Criteria:

• Patients who have used a PPI within 14 days prior to randomization, including over-the-counter Prilosec®.
• Patients who have used any prescription or over-the-counter treatment for symptoms of gastroesophageal reflux disease (GERD), such as Histamine 2 Receptor Antagonists (H2RA) or prokinetics, within 3 days prior to randomization. Antacids may be used, except for those containing bismuth.
• Patients with a known hypersensitivity, allergy, or intolerance to any component of esomeprazole or omeprazole.