Based on self-determination theory, this study tests a model positing that perceived autonomy support from parents and health care providers positively predicts self-efficacy and autonomous self-regulation in dietary self-care. In turn, self-efficacy and autonomous self-regulation predict better dietary self-care over time.Longitudinal data were collected in a consecutive series of 289 adolescent patients with type I diabetes at two time points separated by a two-year interval.Structural equation modeling analysis revealed that perceived autonomy support from health care providers at Time 1 (T1) positively predicted self-efficacy and autonomous self-regulation at Time 2 (T2), T1 self-efficacy and autonomous self-regulation positively predicted T2 dietary self-care, and T1 dietary self-care positively predicted T2 autonomous self-regulation.Autonomy support from health care providers appears to help adolescents develop motivational factors for dietary self-care and adhere to dietary recommendations.