OBJECTIVES: Cost of illness (COI) studies can identify and measure all the costs of a particular disease, including the direct, indirect and intangible dimension. They provide estimates about the economic impact of costly disease. Alzheimer disease (AD) is a relevant example to review cost of illness studies because of its costliness. The aim of this study was to review relevant published cost studies of AD to analyze the method used and to identify which dimension had to be improve from a methodological perspective METHODS: We described the key points of cost study methodology. Cost studies on AD were systematically reviewed. The methodological choices of the studies that estimating AD costs were analyzed using an analytical grid which contains the main methodological items of COI studies. RESULTS: Seventeen articles were retained. Depending on studies, annual total cost of AD per patient varies from $2,935 to $52,954.Disease definition was made mainly with NINCDS-ADRDA criterion and with MMSE for severity stage. The societal perspective was the mainly used perspective and both direct costs and informal costs were assessed in 14 studies. A Prospective record was realized in 13 studies with a bottom-up approach. Resource consumption was mainly estimate with questionnaires. Valuation of unit costs was mostly made with national estimates, reimbursement tariffs and gross wage of a close substitute. Most studies present results clearly and consistently set out in relation to the methods adopted. Nevertheless, methods, data sources, and estimated cost categories in each study varied widely. The review showed that cost studies adopted significantly different approaches to estimate costs of AD, reflecting a lack of consensus on the methodology of cost studies. CONCLUSIONS: Commenting on these quantitative results is problematic because of the different approaches adopted to assess AD costs. To increase its credibility, closer agreement among researchers on the methodological principles of cost studies would be desirable.