This article provides an outline for a cost-effectiveness analysis of a drug that slows the consequences of Alzheimer's disease. Such an analysis cannot easily be performed for 2 main reasons. The first is that often relatives and friends, rather than professionals, take care of the patient. This means that informal care plays an important role in the analysis. However, consensus on how to value informal care is lacking. In this article, we have recommended the shadow-price method because this is an option that can be practically applied. The second reason is that the primary source of information on quality of life, the patients themselves, is unreliable because of cognitive disturbances. The solution is to ask 'significant others' to indicate quality of life instead of the patient. As well as measuring the patient's quality of life, the quality of life of the informal caregiver is also often measured. This is recommended here, but as a separate item in the analysis. In this way, double-counting in the final cost-effectiveness ratio can be avoided. Several instruments for measuring a patient's and caregiver's quality of life are discussed and recommendations about suitable methods are made.