A full upper- and lowercase visual similarity matrix is presented for a standard set of com- puter characters, implemented on the Apple-Psych system. The 2,704 (52 × 52) letter pairs were rated by 12 subjects each. From the ratings, generation and veridical similarity values are derived, and they are tabled for use in research on mixed-case letter matching. In addition, the results of multidimensional scaling and cluster analyses are presented, which give complementary, simplified descriptions of the data.