This study examines whether technically "anonymous" comments entered by participants during group support system (GSS) brainstorming sessions are, in fact, unidentifiable. Hypotheses are developed and tested about the influences of comment length, comment evaluative tone, duration of group membership, and prior communication among group members on the accuracy of attributions they made about the identity of the authors of these technically anonymous comments. Data on prior communication and group history about each of the 32 small groups was collected before participants began using a GSS for brainstorming. Immediately after the session, each member was asked to attribute authorship to a sample of the session's anonymous comments (comment authorship was known to the researchers). The study's participants made attributions that were significantly more accurate than chance guessing. Factors that had a positive influence on attribution accuracy include evaluative tone of comments (especially humorous comments) and amount of prior communication received from other group members. Vividness of comment tone and comment length was not significantly correlated with attribution accuracy. Although the attributions of anonymous comments were more accurate than expected by chance, most of the attributions were incorrect. Implications and consequences of both accurate and inaccurate attribution are discussed along with suggestions for future research.