Regarding the role of metacognition as a promoting factor in language learning and the importance attached to learner autonomy in the literature, this study sought to examine the reliability and validity of self- assessment as an instrument that can make a great contribution to these areas as well as the area of assessment itself. To carry out the study, two intact groups were selected. The first group included 91 applicants for TOEFL classes participating in a TOEFL placement test. The second group involved 43 students of the English Language and Literature at Tehran University. Both groups were asked to self-assess themselves in regard to listening, grammar and reading comprehension. The self- assessment phase was followed by an actual TOEFL test given to both groups for the purposes of this study. The analysis of the data so gathered revealed that self-assessment has acceptable indices of reliability and validity and that such factors as language proficiency and gender had almost no perceivable effect on the reliability

and validity of self-assessment. However, knowledge of the test to be used to compare the go-togetherness of the results of self-assessment and those of an actual test resulted in a considerable difference in the degree of validity.