We examine the confidence and accuracy with which people make personality trait inferences and investigate some consequences of the hypothesis that such judgments are based on similarity or conceptual relatedness. Given information concerning a target person's standing on three global personality dimensions, American and Israeli subjects were asked to estimate the target's self-ratings of 50 trait adjectives and to express their confidence by setting a 90 percent uncertainty range around each estimate. The estimates were positively correlated with the actual ratings obtained from subjects who had evaluated themselves in terms of the 50 traits, but were far too extreme. Furthermore, confidence was negatively correlated with accuracy: People's estimates were most inaccurate and made with greatest certainty when the trait in question was highly similar to the information provided as a basis for judgment. We suggest that intuitive personality judgments overestimate the coherence of the structure underlying trait constructs.