The efficacy of 400 micrograms misoprostol daily in the prevention of NSAID (non-steroidal anti-inflammatory drug)-induced gastric ulcer has been proven. We calculated the cost-effectiveness of a 3-month course of treatment of 200 micrograms twice daily for patients of the sick fund "Wiener Gebietskrankenkasse", based on charges of the year 1993. Since efficacy in preventing NSAID-induced gastric ulcers has not yet been proven for any other drug, we compared misoprostol-treated patients with untreated controls. The model was based on the following assumptions: 70% compliance with respect to misoprostol treatment, 5.6% incidence of gastric ulcer in patients protected with misoprostol, 21.7% incidence among unprotected NSAID users, 20% hospitalisation among patients with gastric ulcer. When using "Kassenpreis" (drug price paid by the sick funds) misoprostol treatment is cost-effective at costs of AS 64,100,--for inpatient care, upwards and at costs of AS 43,361,-upwards when using "Apothekeneinstandspreis" (drug price paid by pharmacies to wholesalers). In Austria costing system of inpatient care is based on a per diem fee. In 1993 the above costs corresponded to an average of 13 and 9 days, respectively, of inpatient care in Vienna. But costs of care increase by almost 25% per year and, hence, this conclusion is only temporarily valid and already in 1994 cost-effectiveness will be reached in less days of inpatient care. Sensitivity analysis shows that cost-effectiveness mainly varies according to the incidence of gastric ulcer among unprotected adults, and the hospitalisation rate of gastric ulcer patients. Efficacy (gastric ulcer rate among misoprostol treated patients) and compliance have a relatively low impact.(ABSTRACT TRUNCATED AT 250 WORDS)