Using a multiple-probe, single case research design, this study investigated the effects of an integrated mindfulness intervention on counselors' negative countertransference while working with children exhibiting externalized behaviors in session. More specifically, this study utilized a two-pronged intervention including mindfulness practices as well as the theoretical tenets of relating to children to assist counselors in managing negative countertransference as measured by the "Countertransference Management Scale" (Perez-Rojas, et al., 2017), reducing negative countertransference feelings as measured by "Therapist Appraisal Questionnaire" (Cooley & Klingler, 1989; Fauth et al., 1999), and improving the child's perception of the counselor as measured by "Young Child Session Rating Scale" (Duncan et al., 2006). The results of this study provided further support for using a two-pronged approach of mindfulness and theory to best manage countertransference and reduce countertransference feelings for counselors working with challenging populations. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]