This study examined the relationship between subjects' actual test derived scores and their estimates of what those scores would be. Fifty-six subjects completed three questionnaires (Morningness-Eveningness Questionnaire; FIRO-B; Myers—Briggs Type Indicator MBTI), and then estimated the scores on each dimension (15 in all) for themselves and another person that they knew well. The results showed significant positive correlations on 10 of the 15 dimensions for themselves. The dimensions that they were best at estimating were Morningness-Eveningness; Extraversion, and Thinking on the MBTI; and Wanted and Expressed Inclusion on the FIRO-B. Eight correlations reached significance concerning their ability to predict another known person's scores but were lower than for their own estimate-actual score correlations. Whereas subjects believed that they were like the other person they nominated (12 of the 15 correlations were significantly positive), in actual fact their test derived scores showed only five significant findings, two positive and the others negative. The results are discussed in terms of lay theories of personality and their relationship to personality assessment.