Aim: To evaluate the relationship between 24- h blood pressure ( BP) measurements and diastolic heart function evaluated by Doppler tissue imaging and B- type natriuretic peptide ( BNP) levels in children with type 1 diabetes mellitus ( DM). Patients and methods: A total of 32 diabetic and 18 healthy children were enrolled. Spectral Doppler analysis and tissue Doppler measurements were performed by conventional echocardiography. The 24- h ambulatory BP and serum BNP levels were measured. Results: Analysis of ambulatory blood pressure monitoring ( ABPM) recordings showed that median daytime diastolic BP load were significantly higher in diabetic patients compared to controls [ 12.35 ( 4.23- 27.23) vs. 2.5 ( 0- 8.7), p= 0.007]. Patients with elevated daytime systolic and diastolic BP loads had significantly higher BNP values compared to patients with normal BP load ( 31.4 +/- 24.36 vs. 11.84 +/- 11.25 pg/ mL, p= 0.03 and 23.21 +/- 15.12 vs. 12.12 +/- 14.65 pg/ mL, p= 0.03, respectively). Isovolemic contraction time ( 47.43 +/- 7.84 vs. 42.27 +/- 7.47, p= 0.045), isovolemic relaxation time ( 68.84 +/- 10.43 vs. 58.77 +/- 10.02, p= 0.02), and myocardial performance index ( 0.45 +/- 0.10 vs. 0.37 +/- 0.09, p= 0.02) as determined by tissue Doppler echocardiography were significantly high in diabetic patients compared to that of control cases. Ratio of mitral peak early diastolic flow velocity ( E) to peak early diastolic myocardial velocities by tissue Doppler echocardiography ( E') was also higher in patients with elevated daytime systolic BP load ( E/ E ', 6.71 +/- 1.97 vs. 4.91 +/- 1.02, p= 0.04). Conclusion: Elevated BP loads detected by 24- h ambulatory BP measurements in children with type 1 diabetes are associated with increased BNP levels and abnormal tissue Doppler echocardiography indices, indicating early stage cardiac dysfunction.