Mindfulness meditation training has been shown to reduce stress and improve short-term memory for military personnel. However, no studies have investigated the effects of in-person and virtual world (VW) mindfulness training on Post-Traumatic Stress Disorder (PTSD) or Attention Deficit Hyperactivity Disorder (ADHD) symptoms. In this study, U.S. military active duty service members and veterans were pseudo-randomized into two mindfulness training groups: in-person (IP) and online via a VW, and a wait-list control group. Volunteers answered a demographic questionnaire, and completed the PTSD Checklist-Military Version (PCL-M) and ADHD Current Symptoms Scale before and after training. The results showed practical and clinically relevant reductions in PTSD symptoms, particular for the IP group, but did not show statistical relevance with hypothesis testing. Results also showed post-training reductions in ADHD symptoms for both IP and VW groups, but no change for the control group. To investigate the effects of initial ADHD symptoms, IP and VW groups were combined into a single Mindfulness Training group. Those with high-initial ADHD symptoms attending training showed improvements, but the control group did not. These results expand research on the mindfulness training, and suggest that IP mindfulness training, rather than VW training, may be of greater benefit for those with PTSD symptoms, while either delivery system appears adequate for reducing attentional symptoms.