People tend to overestimate their capacity to detect lying in others and to underestimate their own ability to tell lies. These biases were demonstrated in a sample of 60 police officers. In a lie-detection task, the officers evaluated their accuracy as high and were overconfident in their judgements. In fact, their performance was below chance level. Participants also received false feedback about their performance. When the feedback suggested that they had performed better than they thought, this further enhanced their perceived lie-detection capacity and also increased their belief in their ability to conceal their own lies. When the feedback suggested they had performed worse than they thought, their ratings of both lie detection and their lie-telling abilities were lowered. Results are discussed in terms of anchoring, availability, and the self-assessment bias. On a practical level, the tendency of police interrogators to overestimate their ability to detect deception could change suspicion into certainty and increase the risk of a false confession. Copyright © 2003 John Wiley & Sons, Ltd.