Many intelligent, capable, and successful individuals believe that their success is due to luck and fear that they will someday be exposed as imposters. A puzzling feature of this phenomenon, commonly referred to as imposter syndrome, is that these same individuals treat evidence in ways that maintain their false beliefs and debilitating fears: they ignore and misattribute evidence of their own abilities, while readily accepting evidence in favour of their inadequacy. I propose a novel account of imposter syndrome as an instance of self-deception, whereby biased evidence treatment is driven by the motivational benefit of negative self-appraisal. This account illuminates a number of interconnected philosophical and scientific puzzles related to the explanation, definition, and value of imposter syndrome