With New Public Management came the idea that public organizations should be led by professional managers, rather than by professionals. This has been referred to as new managerialism. This article explores how new managerialism may affect professional autonomy in a public organization that enjoys a high – and constitutionally protected – degree of organizational autonomy. A framework distinguishing between organizational and occupational professionalism is adopted, in a 10-year case study of the Swedish National Audit Office (SNAO). The study shows how the autonomy of professionals at the SNAO was highly restricted, while management control systems were continuously expanded. At the same time, SNAO performance has been reduced. For example, the SNAO has been criticized for its high overhead costs. The study presented in this article, shows the complex interplay between professionalism, new managerialism, and organizational performance. Based on the findings from this study, the article maintains that it is equally important to consider how autonomy is distributed within agencies, as it is to consider how autonomy is distributed between the political sphere and the administration, when trying to explain organizational performance.