Twitter.com is a "micro-blogging" website. Although Twitter use is growing rapidly, little is known about health behavior discussions on this site, even though a majority of messages are publicly available. We retrieved publicly available Twitter messages during a 5-week period in early 2012, searching separately for the terms "Pap smear" and "mammogram." We used content analysis to code each 140-character message, generating a separate coding framework for each cancer screening term and calculating the frequencies of comments. Using the brief account description, we also coded the author as individual, organization, or news media outlet. There were 203 Pap smear and 271 mammogram messages coded, over three fourths of which were from individual accounts. Overall, 22 % of Pap smear messages and 25 % of mammogram messages discussed personal experiences, including attending appointments, negative sentiment about the procedure, and results. Other messages from both individuals and organizations (8 % Pap smear, 18 % mammogram) promoted screening. About one quarter of the messages expressed personal experiences with cancer screening. This demonstrates that Twitter can be a rich source of information and could be used to design new health-related interventions.