["Scandinavian Journal of Psychology, EarlyView. ", "\nABSTRACT\nResearchers typically rely on self‐report when investigating individuals' behavior. However, when assessing socially undesirable behaviors such as dishonesty, self‐report is vulnerable to underreporting and positive response bias (“faking good”). The present study examined whether supernormality, an extreme form of positive response bias, influences self‐reported lying behavior. A total of 777 participants completed an online survey assessing supernormality and different dimensions of lying behavior. Based on their scores on the Supernormality Scale‐Revised (SS‐R), participants were categorized into a “supernormal group” (n = 223, 28.7%) or a “credible group” (n = 554, 71.3%). Group differences across several lying‐related outcomes were examined. Compared to the credible group, the supernormal group reported lower lying frequency, greater unwillingness to lie due to negative internal factors (i.e., higher negativity), lower contextuality, and lower relational and antisocial lying. These differences emerged consistently across multiple dimensions of lying, suggesting a systematic shift in responding rather than isolated effects. The findings suggest that extreme positive response bias may extend beyond the underreporting of psychological distress to socially undesirable behaviors such as lying, potentially leading to systematic underestimation in self‐report research. Overall, the results highlight the vulnerability of self‐report when assessing sensitive behaviors and the importance of accounting for response bias.\n"]