Dialectical Behavior Therapy's Core Mindfulness skills have the potential to help incarcerated adolescents reduce diverse symptoms of psychopathology. Due to the current lack of research on the independent effect of the Core Mindfulness skills, two studies were performed to examine the effectiveness of a modified Core Mindfulness skills training program in reducing symptoms of depression, anxiety, anger, and suicidal ideation in a sample of incarcerated adolescent females ("students"). In Study 1, eight students completed five self-report measures at three time points. The first two assessments were conducted prior to the treatment, and the third assessment was collected upon completion of the treatment. A series of analyses of variance (ANOVAs) revealed no significant changes in the outcome variables, although there was a slight trend of decreasing scores in the hypothesized direction. In Study 2, 38 students completed two self-report measures prior to and upon completion of the modified Core Mindfulness skills training program, and they provided feedback about the treatment. Additionally, staff members provided behavioral ratings, and group leaders and co-leaders provided feedback about the overarching modified DBT program. Multivariate analyses of variance (MANOVAs), ANOVAs, and Friedman tests revealed significant reductions in student-reported levels of depression, anxiety, and suicidal ideation. There were no significant changes in staff ratings of student behavior. Limitations and contributions of the study are discussed, as well as barriers to successful implementation of treatment research in a correctional facility. Recommendations to improve treatment implementation in secure settings, and suggestions for future research are offered.