Literature on emergency department (ED) crowding and boarding has primarily focused on adverse patient outcomes including increased patient mortality, and longer hospital length-of-stay. Few studies have explored relationships between ED crowding, boarding and physician wellbeing (burnout, professional satisfaction) despite evidence demonstrating that EM specialists are consistently among those with the highest rates of burnout. Therefore, we sought to evaluate the relationships between markers of ED crowding and boarding and physician wellbeing. Data for this prospective, observational study were collected from resident and attending emergency physicians employed at our Level-I, tertiary care referral center ED. Participants completed the 7- item Physician Well-Being Index (PWBI) twice weekly for three months following clinical shifts. The PWBI assesses physician distress across several dimensions using a score from 0 to 7 and has previously demonstrated validity with similar physician groups. For the same period, we collected markers of ED crowding and boarding: ED volume, numbers of arriving and boarding patients by shift, and average census by shift. Generalized Estimating Equations (GEE) analyses were performed to examine relationships between ED crowding and boarding markers and physician PWBI scores. Hierarchical regression models were constructed to control for the potentially confounding effects of the day of the week, shift type, and provider role (resident/attending). 42 emergency physicians (18 (43%) resident, 24 (57%) attending) participated in the study, providing 273 PWBI assessments. Data for 4, 318 ED patient encounters were summarized for the same period. Mean PWBI scores were 2.3 (SD 1.53, 95% CI: 2.1-2.5); no significant differences between the resident and attending groups were noted (2.0, ±1.50, 95% CI: 1.5-2.6 vs. 2.5, ±1.52, 95% CI: 1.9-3.0, respectively). After adjusting for the effects of day of week, shift type, and provider role, we did not observe statistically significant relationships between PWBI scores and count of arrivals in 24 hours (b=-0.089, SE=0.0593, CI: -0.206-0.027, p=0.133), patient arrivals by shift (b=-0.006, SE=0.013, CI: -0.031-0.02, p=0.667), average census by shift (b=0.004, SE=0.019, CI: 0.041-0.047, p=0.829), or average boarding census by shift (b=-0.161, SE=0.1051, CI: -0.367-0.045, p=0.127). In this study, ED crowding and boarding were not significantly related to physician wellbeing, as measured by the PWBI. Findings suggest further research is needed to validate the PWBI in capturing ED physician wellbeing during periods of ED crowding and boarding. Next steps are to explore the relationships between individual dimensions of wellbeing (fatigue, mental quality of life) and ED busyness, given the important impact of dimensions of burnout on care team wellbeing and patient outcomes.