This exploratory study contributes to research on relevance assessment by specifying criteria that are used in the judgment of information quality and credibility in Internet discussion forums. To this end, 4,739 messages posted to 160 Finnish discussion threads were analyzed. Of the messages, 20.5% contained explicit judgments of the quality of information and credibility in other messages. In the judgments, the forum participants employed both positive criteria such as validity of information and negative criteria such as dishonesty in argumentation. In the evaluation of the quality of the message's information content, the most frequently used criteria pertained to the usefulness, correctness, and specificity of information. In the judgment of information credibility, the main criteria included the reputation, expertise, and honesty of the author of the message. Since Internet discussion forums tend to emphasize the role of disputational discourse questioning rather than accepting the views presented by others, mainly negative criteria were used in the judgments. The generality of our claims is limited because we chose forums that focused on sensitive and value-laden topics; future work could explore credibility and quality judgment in other forums and forumlike venues such as question and answer sites as well as exploring how quality and credibility judgments interact with other aspects of forum use.