Lansoprazole is a proton pump inhibitor that inactivates the H(+)/K(+)-ATPase pump in parietal cells, thus inhibiting gastric acid secretion and increasing intragastric pH. In an open-label, uncontrolled trial in children aged 1-11 years with gastro-oesophageal reflux disease (GORD), treatment with lansoprazole 15 or 30 mg (depending on weight) once daily for 8-12 weeks improved symptoms compared with baseline in 76% of patients (47 of 62) based on patient diaries and healed erosive oesophagitis (confirmed endoscopically) in all 27 children who had it at baseline. In adolescents aged 12-17 years with GORD, 8 weeks' treatment with lansoprazole 15 mg (in 64 patients with non-erosive disease) or 30 mg (in 23 patients with erosive oesophagitis) once daily reduced the frequency and severity of symptoms by 63% and 69% compared with baseline, based on patient diaries. In this open-label, uncontrolled trial, 96% of evaluable patients with erosive disease (21 of 22) had mucosal healing by week 8, as confirmed by endoscopy; mucosal healing did not occur after an additional 4 weeks' treatment in one patient. Lansoprazole was generally well tolerated in children and adolescents, with the most common treatment-related adverse events being gastrointestinal events and headache.