RESUMO
This paper examines the use of 'mystery guests' as an instrument for monitoring quality and safety in healthcare. The Dutch Health Inspectorate initiated a mystery guest pilot project in elderly care as a response to political and social pressure. An independent evaluation of this project revealed that the primary goal of this approach--to provide a better view of the exigencies of daily practice in elderly care--was not met. Inspectors did not use the information delivered by the mystery guests because how they evaluated quality and reported findings did not align with practices used by the health inspectorate. Additionally, the inspectors felt that other instruments being developed were more appropriate for providing a better view of practice. While political pressure is important for effecting change in general, the specific instruments to be used for formal supervision of health institutions should be developed and implemented within the organization in accordance with existing standards and approaches. The choice to implement a new supervision instrument, including sending mystery guests into care institutions, should be preceded by an ethical analysis that takes into account the specific context of its use.