Good clinical decision-making is important in dermatologic surgery. Experience and knowledge help considerably, but take time to acquire. However, how the clinician thinks is also a significant contributory factor. How we think is influenced by many factors, including our beliefs, prejudices, confidence and variables like how we are feeling at that moment physically and emotionally. Thought process can be either fast and subconscious or slow and analytical. Fast thinking contributes to the majority of decision-making and is especially prone to a range of biases which may contribute to suboptimal clinical outcomes. We wish to highlight and illustrate common biases in thinking encountered by the dermatologic surgeon.</p