This study compared the cost-effectiveness of meropenem with that of imipenem plus cilastatin in the treatment of severe infections in hospital intensive care in the UK. A Markov model was constructed to model lifetime costs and quality-adjusted life years (QALYs) of using meropenem and imipenem plus cilastatin for the treatment of severe infections in intensive care. Estimates of effectiveness, utility weights and costs were obtained from the published literature. Probabilistic sensitivity analysis was conducted to assess the robustness of the results. Estimated treatment costs for the patient cohort were pound 14,938 with meropenem and pound 15,585 with imipenem plus cilastatin. QALYs gained were 7,495 with meropenem and 7,413 with imipenem plus cilastatin. Probabilistic sensitivity analysis showed meropenem to be significantly less costly (-pound 636.47, 95% CI -pound 132.33 to -pound 1,140.62) and more effective (0.084, 95% CI 0.023 to 0.144). Meropenem thus appears significantly more effective and less expensive than imipenem plus cilastatin and should therefore be considered the dominant treatment strategy.