This paper investigates the role of some selected psychological and personality traits of learners of English as a foreign language in the accuracy of self- and peer-assessments. The selected traits were motivation types, self-esteem, anxiety, motivational intensity, and achievement. 78 students of English as a foreign language participated in thirteen-week oral presentation tasks, during which they were asked to assess their own performance and that of their peers. The study concludes that assessment is a multifaceted process, which is affected by various psychological and personality traits of the raters. The results of the study seem to fall in line with the general pattern that learners possessing the positive side of a trait are more accurate than those who have its negative side, with the exception of students with high classroom anxiety. In addition, high reliability indices similar to those reported in the literature are obtained. The study also shows that long periods of practice and sufficient feedback have a positive effect on the accuracy of assessment. Finally, the study demonstrates that students with low self-esteem are the most accurate in assessing their performance, whereas learners with instrumental motivation are the least accurate.