Objective: To evaluate progression of left ventricular (LV) structural and functional changes in patients with type 1 diabetes and effect of glycemic control on these changes. Materials and Methods: A prospective, longitudinal study consisted of 48 patients who were originally studied. At two years follow-up, 44 patients were reevaluated, 35 patients from the original study were reevaluated after another 2 years for the 3rd time using the same protocol. The control group comprised 30 age-and sex-matched healthy volunteers. All studied patients were subjected to full history taking, clinical and cardiac examination. M-mode echocardiography was done, blood samples were taken and examined for HbA1c and urine samples were tested for the presence of albuminuria. ANOVA for repeated measurements, t-test for dependent and independent variables, and Mann-Whitney U test were used for statistical analyses. Results: Seven (14.6%) of our patients had LV hypertrophy, 23 (47.9%) patients had diastolic dysfunction and ten patients only achieve improvement in glycemic control. Duration of diabetes was significantly higher in patients with LV hypertrophy (LVH) (p<0.05). Patients with no improvement in glycemic control had a significant increase in interventricular septum (IVS) and left ventricular posterior wall (LVPW) in the third examination (p<0.05 for both). Conclusion: Prevalence of LVH and diastolic dysfunction among diabetic patients is high. Glycemic control in diabetic patients could not improve LVH or diastolic dysfunction. On the other hand, failure to achieve glycemic control leads to deterioration in structural parameters.