BACKGROUND: A new drug is approved for use if its effectiveness has been demonstrated. Recently decision makers in a number of countries have begun to account for both the effectiveness and cost-effectiveness of new drugs. However, cost-effectiveness evidence lags behind the effectiveness data. OBJECTIVE: To explore the timeliness of delivering cost-effectiveness information about new drugs with established effectiveness and significant financial impact. METHODS: New drugs were identified, based on guidance documents and reports published by the National Institute for Clinical Excellence of England and Wales, and the following data were collected: dates of publication of first effectiveness and cost-effectiveness evidence, methodology of the cost-effectiveness analysis, funding of the research, etc. RESULTS: Guidance documents for the following new drugs/drug groups have been published by NICE by the end of 2000: taxanes for ovarian and breast cancer, proton pump inhibitors in the treatment of dyspepsia, glycoprotein IIb/IIIa inhibitors, methylphenidate for hyperactivity in childhood, zanamivir, and rosiglitazone for type II Diabetes Mellitus. The analysis of the evidence shows that the effectiveness of these drugs has been demonstrated in the last 12 years. However, cost-effectiveness evidence has been published for 70% of the drugs with an average delay of 3 years (range 0-10). The cost-effectiveness of those, introduced after 1995 (80% of all included drugs/drug groups), has been demonstrated using models only, if at all. CONCLUSIONS: Cost-effectiveness evidence is produced with a lag behind the effectiveness evidence. As a result, decision makers are in a position of awaiting sound evidence while issuing guidance based on current inconclusive research results. The cost to society is discussed, and establishing the cost-effectiveness of new drugs alongside RCTs at an earlier stage of their development is suggested.