AIM: Rotavirus is the leading cause of acute gastroenteritis in children. Two rotavirus vaccines (RotaTeq and Rotarix) have recently completed clinical trials. We investigated whether routine infant immunisation with either vaccine can be cost effective. METHODS: We compared costs and outcomes of vaccination using a cohort model, following children over the first 5 years of life. We estimated health provider costs, economic costs and quality adjusted life years (QALYs) lost due to rotavirus-related deaths, hospital admissions, nosocomial infections, accident and emergency attendances, general practice consultations and calls to NHS Direct. RESULTS: Under base case assumptions, a programme using RotaTeq (priced at pound 25 a dose) would cost the health provider pound 79,900 per QALY gained. Using Rotarix (priced at pound 35 a dose) would cost pound 61,000 per QALY gained. Univariate and multivariate sensitivity analysis indicate that at these prices an immunisation programme would be unlikely to be cost-effective for any realistic value of the key parameters. CONCLUSIONS: Rotavirus immunisation could reduce the substantial short-term morbidity burden due to rotavirus, but is unlikely to be deemed cost effective unless the vaccine is competitively priced.