Smoking cost the National Health Service (NHS) in England in 1996 an estimated £1.4-£1.7 billion. In 1998, in Smoking Kills, the Government outlined an action plan for reducing smoking prevalence. This paper estimates 2006 costs and the impact of declining prevalence. Estimates are derived from costs, service use, and attributable proportions based on current and ex-smokers' prevalence and relative risk compared with never-smokers. Comparable 1996 costs were estimated by substituting 1996 prevalence. Smoking-attributable hospital admissions cost the NHS an estimated £1 billion in 2006, outpatient attendances cost £190 million, general practitioner (GP) consultations £530 million, practice nurse consultations £50 million and GP prescriptions £900 million; £2.7 billion in total. This represents 5% of adult hospital admission costs, 4% outpatients, 11% GP and 8% practice nurse consultations and 12% of prescription costs. Smoking accounted for 24% of respiratory disease hospital admission costs and 16% of cancer and cardiovascular disease costs (people aged ≥ 35 years). The 2006 cost is estimated to be 13% lower than if smoking had remained at 1996 levels. Smoking represents a substantial cost throughout the NHS. Significant savings are associated with a reduction in prevalence, but much of this stems from an earlier phase of the smoking epidemic. Securing future such savings requires further policies to reduce smoking prevalence.