Monetary valuation of health impacts is increasingly used to support decision process, often relying mainly on economic criteria, and to take into account preferences of concerned people. This use leads to questioning the reliability of the methods and their adaptation to the context of decisions support. This work aims at determining the robustness of monetary values of health impacts estimated by contingent valuation via the following question: does the cause of the assessed health impact influence its monetary value? Economic theory outlines that, on the one hand monetary value of an health impact should depend on its characteristics only and not on its causes, on the other hand all information useful to the valuation should be provided. In practice, contingent valuations sometimes state the causes, with inconsistent results. A contingent valuation was conducted to analyze the effect of cause of chronic obstructive pulmonary disease, with four versions of the questionnaire: the cause is not indicated, the causes are said to be mainly smoking and air pollution, the cause is said to be air pollution only, and smoking only. Results show that stipulating the possible causes increases the acceptability of the questionnaire. The willingness to pay depends less on the causes but more on the personal characteristics of the respondents, especially their health and environment (healthy diet, sport practice, pollution in living area). To conclude, providing information about the causes of the valued health impact would increase the reliability of the assessment. Uncertainties remain high in particular as this valuation stays unusual in France where the National Health Service covers most of health expenses.