Confirmation bias is a pitfall in emergency care and may lead to inaccurate diagnoses and inappropriate treatments and care plans. Because of the increasing severity and volume of emergency care, emergency physicians often must rely on heuristics, such as rule-out protocols, as a guide to diagnosing and treating patients. The use of heuristics or protocols can be potentially misleading if the initial diagnostic impression is incorrect. To minimize cognitive dissonance, clinicians may accentuate confirmatory data and ignore nonconfirmatory data. Clinicians should recognize confirmation bias as a potential pitfall in medical decision making in the emergency department. Reliance on the scientific method, Bayesian reasoning, metacognition, and cognitive forcing strategies may serve to improve diagnostic accuracy and improve patient care.