Diabetes mellitus (DM) is now the sixth leading cause of death in the U.S., primarily due to cardiovascular (CV) complications. People with DM have a 2 to 4 times increased risk for heart disease. An increasing number of adolescents are diagnosed with DM, predisposing them to CV morbidity and mortality in early adulthood. Using a comparison group pretest-posttest design, the Primary Aim of this investigation is to determine the feasibility of conducting a novel personalized exercise prescription (PEP) intervention with 20 adolescents who have type 1 DM and 20 adolescents with type 2 DM. We will explore the influence of DM-specific family social support, exercise self-efficacy, and benefits and barriers to exercise on adherence to PEP. The Secondary Aim is to explore possible changes in physiological (i.e., cardiorespiratory fitness, heart rate variability, metabolic control, and lipid profile) and psychological outcomes (i.e., diabetes quality of life [QOL]) of the PEP intervention in adolescents with type 1 or type 2 DM. Long-term benefits of exercise for persons with DM include decreased risk factors for CV disease, improved well-being, and increased life expectancy. The current decline in physical activity during adolescence is problematic, particularly for those with DM, who have an added risk for future CV disease. The limited research available on the efficacy of exercise interventions with youths who have type 1 DM indicates improvements in cardiorespiratory fitness, lipid profile, and glucose regulation. No published exercise intervention research with adolescents who have type 2 DM is available. However, exercise interventions with overweight youth have shown increased heart rate variability and cardiorespiratory fitness. Although numerous studies have examined various school-based strategies to promote more physically active lives in youth populations, no studies have examined the feasibility of conducting individualized, culturally focused exercise prescriptions for adolescents with type 1 or type 2 DM that incorporate family support in a home or community setting. Nor have studies addressed the possible psychosocial and physiological outcomes of these personalized approaches. This investigation will extend the principal investigator's program of research that identified differences in CV risks for adolescents with type 1 vs. type 2 DM. Determining factors that influence the conduct and outcomes of individualized exercise interventions for adolescents with DM can potentially lead to the development of programs that promote adherence to exercise, avert complications, and improve QOL and overall health.