Infectious disease specialists are frequently consulted for diagnostic and therapeutic advice on challenging cases. When evaluating patients, the infectious disease specialist is well positioned to offer an appropriate diagnostic approach but is also at risk of not recognizing the correct diagnosis for a variety of reasons. We believe it is important to provide infectious disease specialists and trainees with a fundamental understanding of diagnostic errors, clinical reasoning, and cognitive biases. We present 2 cases demonstrating common cognitive biases leading to diagnostic errors, and we reflect on strategies that may aid in their prevention. We hope to provide knowledge and tools that may help prevent diagnostic errors in the future. © The Author 2013.