Objective: Since post-traumatic stress disorder (PTSD) is common after military deployment and affects both military service members and their families, we sought to both improve PTSD-related knowledge of military family members and to foster actions to help service members with their symptoms. Methods: Focus groups were conducted with military family members and their feedback was incorporated into an educational Web site to improve family members' knowledge of PTSD. We pilot-tested the site and a 25-item questionnaire, then used it to assess the knowledge of 497 family members before and after their use of the Web site. Results: Use of this educational Web site improved military family members' PTSD-related knowledge on a 25-item test, with an increase from a mean 13.9 correct responses beforehand to 18.7 after Web site use (p < 0.001; effect size 1.2). In addition, 217 family members returned to the site 310 days after their initial visit; 57% had taken actions such as discussing the service member's symptoms with them or persuading them to get medical attention, and 82 to 95% of them believed their actions to be beneficial. Conclusion: A Web-based intervention can both improve PTSD-related knowledge and foster behavioral changes in military family members.