As more interpersonal interactions move online, people increasingly get to know and recognize one another by their self-selected identifiers called usernames. Early research predicted that the lack of available cues in text based computer-mediated communication (CMC) would make primitive categories such as biological sex irrelevant in online interactions. Little is known about the types of perceptions people make about one another based on this information, but some limited research has shown that questions about gender are the first to be asked in online interactions and sex categorization has maintained salience. The current project was designed to examine the extent to which individuals might include obvious gender information in their usernames, as well as how easily gender could be attributed from usernames. Seventy-five coders were asked whether or not they could assign 298 people to a sex category based only on their username, and then to rate how confident they were in making the attribution. Results indicated that coders were fairly inaccurate in making these attributions, but moderately confident. Additionally, the results indicated that neither women nor men were more accurate in attributing gender from usernames, and that neither women nor men tended to use more obvious gender markers in their usernames. Additionally, those who did use obvious gender markers in their username tended to have less experience with computer chat. The results are discussed in conjunction with the limitations of the present investigation, and possibilities for future research.