Objective:To assess quality of life (QoL) and glycemic control in adolescents with type 1 diabetes and to investigate the impact of an educational program.Methods:A quasiexperimental study with nonrandomized experimental and control groups was conducted in which a total of 503 adolescents with type 1 diabetes completed a questionnaire using the Diabetes Quality of Life Instrument for Youth. Adolescents were then assigned to experimental and control groups. The experimental group was subjected to four 120-minute sessions of an educational program over a period of 4 months. Extracted medical chart data included the duration of diabetes, insulin dosage, and most recent hemoglobin A1c levels. Analysis of covariance was used to detect the impact of intervention.Results:The overall mean QoL score (%) was 76.51 ± 9.79, with good QoL in 38% of all adolescents. Poorer QoL was significantly associated with older age (P < 0.001), more hospital admissions in the last 6 months (P = 0.006), higher levels of depression (P < 0.001), poor self-esteem (P < 0.001), and poor self-efficacy (P < 0.001). There was significant deterioration in all domains of QoL in the experimental group after intervention. However, this deterioration was significantly less severe than in the control group. Between-group effects on total knowledge, adherence to exercise, glucose monitoring, treatment, self-efficacy, family contribution to management, glycemic control, and satisfaction with life were significantly in favor of the experimental group.Conclusion:Education intervention for adolescents with type 1 diabetes could be a safeguard against possible deterioration in QoL and glycemic control over time.