Professionalism can be defined generally as adhering to the accepted standards of a profession and placing the interests of the public above the individual professional's immediate interests. In the field of medicine, professionalism should lead at least some practitioners in developing countries to effectively care for their patients despite the absence of extrinsic incentives to do so. In this study we examine the behavior of 80 practitioners from the Arusha region of Tanzania for evidence of professionalism. We show that about 20% of these practitioners behave professionally, and almost half of those who do so practice in the public sector. These professional health care workers provide high quality care even when they work in an environment that does not reward this effort, a finding that has important implications for the use of performance-based incentives. Copyright © 2009 John Wiley & Sons, Ltd.