OBJECTIVES: Assessing the potential increase in GERD medical treatment expenses and the impact of on-demand treatment with esomeprazole. METHODS: The number of patients with GERD was derived from epidemiological studies. The number of proton pump inhibitor (PPI) users was calculated from IMS publications and reimbursement data provided by sick-funds. According to clinical practice, in future, the number of patients taking a PPI will be the number of weekly GERD sufferers. Alternatively, future PPI users will comprise patients currently receiving a PPI plus those currently using H2-receptor antagonists, plus a large part of current antacids users. Results of on-demand treatment come from the ONE study (2-arm parallel study over a 6-month maintenance period, on-demand versus continuous therapy with esomeprazole 20 mg). RESULTS: A totla of 28% of the Belgian adult population (n=10 million) have GERD symptom(s), 11% weekly, 4% daily. Assuming stable prevalence of GERD over the next decade, the number of PPI-treated patients could reach approximately 920 000/year from 446 000 currently. Yearly expenses would therefore increase from 149€ to 248€million . This would be reached by 2010 with linear growth or 2005 with exponential growth. In 2652 Belgian patients with a similar profile to the screened population of the epidemiological studies, the ONE study showed on-demand treatment (mean daily intake: 0.6 tablet) was similar to continuous treatment (1 tablet/day) for patient satisfaction (92% in both groups), heartburn relapse (11.3% vs. 9.4%, respectively) and GERD-related co-medication intake (8% vs. 7.3%, respectively). Over a 7-month treatment period (4 weeks of acute treatment then 6 months’ maintenance), on-demand esomeprazole 20 mg would save approximately 27.5% on medication costs compared with continuous esomeprazole therapy. CONCLUSIONS: Increasing costs due to the expected increased use of PPI's can be lowered by using an effective PPI with an on-demand approach, which maintains high patient satisfaction and efficacy.