: The provision of healthcare services to patients in primary care practices is a highly chaotic and complex process, which is poorly understood. On average, family physicians deal with 3.05 problems during each encounter; the specific number of problems is highly variable and related to patient age and the presence of underlying medical conditions. Furthermore, the average encounter lasts 17 minutes. Medical errors can thrive in an environment of inattention, competing demands and time stress. Hypothesis: It is hypothesized that the competing demands of multiple patient problems and limited time have a significant effect on clinician mental workload, which, in turn, affects quality of care and propensity for medical error. Goals and Objectives: We will conduct a pilot study to better define the relationships between encounter problem density (number of problems per unit time), clinician mental workload (as ascertained by the NASA Task Load Index), perceived medical error, and quality indicators. The feasibility of collecting this data using physician-medical assistant teams within busy WREN practices will be explored. Methods: Each of 30 recruited WREN physicians will collect data on 20 routine adult patient visits over a four-week period, thus resulting in a sample of 600 visits. Specific data collected will include patient age and gender, the patient's anticipated number of medical issues to be discussed during the visit, clinician mental workload as measured by the post-visit NASA TLX, physician reported number and types of problems addressed, face-to-face time spent during the visit, physician estimated likelihood of error, patient reported extent to which concerns were addressed, and a copy of the resulting clinical note for assessment of quality indicators around blood pressure and tobacco use. Correlations between encounter problem density, clinician mental workload, and perceived medical error will be evaluated. Structured interviews will be conducted with physicians on a subset (n~30) of outlying encounters (i.e., high problem density and low mental workload). Significance: Results of this pilot study will be used to refine a systems model developed by industrial engineers to better define the process of primary healthcare delivery. This will serve as a basis for additional studies of the relationship between complexity and error in family practice and primary care. As this model is better developed, enhancements made at critical points may result is more efficient delivery of care with a reduction in error and improvement in quality. ? ?