Open access services allow direct referral by primary care doctors, without an opinion from a gastroenterologist. Our aim was to measure this new service’s effect on prescribing costs. METHODS: The study used all patients from Tayside who had complete prescribing data for one year before referral and one year after endoscopy and had a diagnosis recorded at endoscopy. The main outcome measure was the change in prescribing costs for dispensed ulcer healing drugs (UHDs) in the four months after endoscopy compared to the four months before referral. RESULTS: Of the1063 patients referred, 883 were resident in Tayside and had complete data. The results of endoscopy were normal in 311 (35%), oesophagitis in 323 (37%), ulcer in 55 (6%), both in 33 (4%) and other upper GI pathology in 161 (18%). Significant independent predictors of prescribing cost after endoscopy were: the cost of drugs before referral, the diagnosis at endoscopy and age (p=0.0001 by both generalised linear modelling and a non-parametric ranking test). Variables that were not significantly associated with prescribing cost after endoscopy were: sex, interval between referral and endoscopy and previous history of either UHDs, endoscopy or hospitalisation for GI event. Controlling for age and cost of drugs before referral, there was a mean decrease in prescribing costs of £11 per patient with normal endoscopy. Prescribing costs increased by £33 for oesophagitis, by £25 for ulcer, by £41 for both and by £23 for other pathology. CONCLUSIONS: Open access endoscopy was associated with increased cost of prescribing for UHDs, mainly because the procedure revealed pathology in 65% of cases. ECONOMIC AND OUTCOMES STUDY RESULTS FOR PULMONARY DISORDERS & INFECTIOUS DISEASE