A four-level taxonomy is proposed to define the usefulness of rater written comments for supporting letters of recommendation. The taxonomy is used to classify comments on 220 rating forms by 25 raters from two surgery departments regarding performance by third-year medical students. Written comments were classified by the following taxonomy: (1) no comment; (2) vague comment (e.g., overall good performance); (3) descriptive comment (e.g., excellent rapport with patients); and (4) behaviorally referenced comment (e.g., excellent rapport with patients as indicated by numerous complimentary comments from patients). Behaviorally referenced comments were deemed the most useful to directors of clerkships. Two reviewers were trained to read and classify the written comments, and interrater reliability was assessed by having the raters read and classify 20 of the same forms. Results indicate that individual raters within a department and departments at separate sites differ in the percentage of written rater comments at each of the four levels. While individual rater differences account for differences in comment types, perceived departmental expectations also appear to influence the levels of written rater comments. There is a 13-item list of references. (SLD)