Background Multitasking is a key skill for emergency department (ED) providers. Yet, potentially beneficial or debilitating effects for provider functioning and cognition are underexplored. We therefore aimed to investigate the role of multitasking for ED physicians’ work stress and situation awareness (SA). Methods Two consecutive, multi-source studies utilizing standardized expert observations in combination with physicians’ self-reports on stress and SA were set out in an academic ED. To control for ED workload, measures of patient acuity, patient counts, and ED staff on duty were included. Regression analyses estimated associations between observed proportion of time spent in multitasking with matched ED physicians’ reports on stress (study 1) and SA (study 2). Results ED physicians engaged between 18.7% (study 1) and 13.0% (study 2) of their worktime in multitasking. Self-reported as well as expert-observed multitasking were significantly associated. This confirms the internal validity of our observational approach. After controlling for ED workload, we found that physicians who engaged more frequently in multitasking perceived higher work stress (Beta = .02, 95%CI .001–.03; p = .01). In study 2, ED physicians with more frequent multitasking behaviors reported higher SA (B = .08, 95%CI .02–.14; p = .009). Conclusions Multitasking is often unavoidable in ED care. Our findings suggest that ED physicians’ multitasking increases stress experiences, yet, may facilitate professional’s experiences of situation awareness. Our results warrant further investigation into potentially ambivalent effects of ED providers’ multitasking in effectively sharing time between competing demands while maintaining performance and safety.