OBJECTIVE Physicians' negative attitudes toward patients with obesity are well documented. Whether or how these beliefs may affect patient-physician communication is unknown. To describe the relationship between patient body mass index (BMI) and physician communication behaviors (biomedical, psychosocial/lifestyle, and rapport building) during typical outpatient primary care visits was aimed. DESIGN AND METHODS Using audio-recorded outpatient encounters from 39 urban primary care physicians (PCPs) and 208 of their patients, the frequency of communication behaviors using the Roter Interaction Analysis System was examined. The independent variable was measured; patient BMI and dependent variables were communication behaviors by the PCP within the biomedical, psychosocial/lifestyle, and rapport building domains. A cross-sectional analysis using multilevel Poisson regression models to evaluate the association between BMI and physician communication was performed. RESULTS PCPs demonstrated less emotional rapport with overweight and obese patients (incidence rate ratio, IRR, 0.65, 95%CI 0.48-0.88, P = 0.01; IRR 0.69, 95%CI 0.58-0.82, P < 0.01, respectively) than for normal weight patients. No differences in PCPs' biomedical or psychosocial/lifestyle communication by patient BMI were found. CONCLUSIONS Our findings raise the concern that low levels of emotional rapport in primary care visits with overweight and obese patients may weaken the patient-physician relationship, diminish patients' adherence to recommendations, and decrease the effectiveness of behavior change counseling.