Purpose. The purpose of this study was to determine whether an adaptation of the Diabetes Prevention Program (DPP) could be successfully implemented in a correctional environment to promote weight loss, lower A1C, and improve other cardiometabolic outcomes. Methods. A quasi-experimental, staggered-start control study was conducted in a female and male federal correctional institution. Twenty-six male and 21 female incarcerated, overweight individuals with prediabetes or at high risk for developing diabetes were randomly assigned to two groups. Data were measured at 6-month intervals starting at baseline for 18 months. Group 1 participated in the 12-month Group Lifestyle Balance intervention program from baseline to 12 months. Group 2 served as a control group from baseline for 6 months and then completed the intervention program from months 6 to 18. Results. Participants were ethnically diverse and mostly >44 years of age. At baseline, members of the two study groups were not significantly different with regard to sex, race/ethnicity, age, or prediabetes status. About half of participants (51%) completed the program, with participants in group 1 significantly more likely to be completers (P Conclusion. The DPP may be an effective method for reducing the impact of diabetes in the correctional environment addressed. Larger studies should be conducted to confirm these outcomes. Study findings were affected by high attrition rates, primarily due to transfers and releases from the institution.