A substantial proportion of diagnostic errors can be attributed to cognitive biases on the part of clinicians. However, few studies have attempted to address these biases systematically. This study, conducted at five Dutch hospitals, attempted to characterize the frequency and severity of diagnostic error in patients presenting with dyspnea (difficulty breathing) and provided structured feedback to physicians who committed such errors. The authors found faults in the diagnostic reasoning process in the majority of patients and overt errors leading to patient harm in 11% of cases. Feedback to clinicians on their diagnostic errors was generally well received. An AHRQ WebM&M interview with Dr. Pat Croskerry discusses the issue of cognitive biases in diagnosis.