Background: Diabetic nephropathy is a leading cause of chronic kidney disease (CKD). This study investigates the impact of renal anatomy on glomerular filtration rate (GFR) in diabetic patients, comparing those with controlled and uncontrolled diabetes. Objective: To evaluate the relationship between renal anatomy (kidney size and cortical thickness) and GFR in diabetic patients and to assess the effect of glycemic control on these parameters. Methods: An observational study was conducted with 100 diabetic patients divided into two groups: controlled diabetes (HbA1c ≤ 7%, n=50) and uncontrolled diabetes (HbA1c > 7%, n=50). Renal ultrasound and MRI were used to measure kidney size and cortical thickness. GFR was estimated using the CKD-EPI equation. Correlations between HbA1c, renal anatomy, and GFR were analyzed. Results:Mean age: 55 ± 10 years.Kidney length: 11.5 ± 0.8 cm (controlled) vs. 12.1 ± 0.9 cm (uncontrolled) (p < 0.05).Cortical thickness: 7.2 ± 0.6 mm (controlled) vs. 6.5 ± 0.5 mm (uncontrolled) (p < 0.01).Mean eGFR: 85 ± 12 mL/min/1.73 m² (controlled) vs. 72 ± 15 mL/min/1.73 m² (uncontrolled) (p < 0.01).Significant negative correlation between HbA1c and eGFR (r = -0.65, p < 0.001).Positive correlations between kidney size and eGFR (r = 0.42, p < 0.01) and between cortical thickness and eGFR (r = 0.50, p < 0.01).Microalbuminuria: 30% (controlled) vs. 60% (uncontrolled) (p < 0.05).Macroalbuminuria: 0% (controlled) vs. 10% (uncontrolled) (p < 0.05). Conclusion: Renal anatomy significantly affects GFR in diabetic patients, with uncontrolled diabetes leading to greater reductions in GFR. Regular monitoring and management of renal health are crucial for diabetic patients.