OBJECTIVE: To assess the cost effectiveness of an immunisation programme for rotavirus-associated gastroenteritis among children aged five years old and under in the United Kingdom. METHOD: Economic evaluation based on a decision analytical model using data from a review of published evidence was used. Incremental cost effectiveness ratios are estimated from both the societal and health sector perspectives. RESULTS: Using conservative vaccine efficacy estimates, current immunisation rates and a vaccine cost of £60 per completed course, rotavirus immunisation would incur a net health sector cost of £27.8 million per birth cohort (£42.52 per child). A vaccination programme could, however, provide net savings to society of £4.8 million; that is, from the societal perspective a programme of vaccinating against rotavirus dominates the alternative of no programme by preventing more cases and costing less. Threshold analysis identified a breakeven price of £13.26 per course, such that any price less than this would also result in cost savings for the health sector. These results are, however, sensitive to a range of variables and, in particular, society's cost savings are negated if parents spend less time away from employment and/or forego less income. CONCLUSIONS: It appears that some of the health sector costs and all of the societal costs of gastroenteritis in children can be avoided by an immunisation programme using one of the two vaccines recently developed. The net cost to the health sector may, however, be considered worthwhile if there is a sufficient improvement in the quality-of-life of children and parents affected by gastroenteritis; this study did not find any evidence of research which has measured the utility gains from vaccination.