BACKGROUND: Assessing the quality of care provided by individual health practitioners is critical to identifying possible risks to the health of the public. However, existing assessment methods can be inaccurate, expensive, or infeasible in many developing country settings, particularly in rural areas and especially for children. Following an assessment of the strengths and weaknesses of the existing methods for provider assessment, we developed a synthesis method combining components of direct observation, clinical vignettes, and medical mannequins which we have termed "Observed Simulated Patient" or OSP. An OSP assessment involves a trained actor playing the role of a 'mother', a life-size doll representing a 5-year old boy, and a trained observer. The provider being assessed was informed in advance of the role-playing, and told to conduct the diagnosis and treatment as he normally would while verbally describing the examinations. METHODOLOGY/PRINCIPAL FINDINGS: We tested the validity of OSP by conducting parallel scoring of medical providers in Myanmar, assessing the quality of their diagnosis and treatment of pediatric malaria, first by direct observation of true patients and second by OSP. Data were collected from 20 private independent medical practitioners in Mon and Kayin States, Myanmar between December 26, 2010 and January 12, 2011. All areas of assessment showed agreement between OSP and direct observation above 90% except for history taking related to past experience with malaria medicines. In this area, providers did not ask questions of the OSP to the same degree that they questioned real patients (agreement 82.8%). CONCLUSIONS/SIGNIFICANCE: The OSP methodology may provide a valuable option for quality assessment of providers in places, or for health conditions, where other assessment tools are unworkable.