Background: This study aimed at documenting the degree of atherosclerosis, which is an important macrovascular complication in Nigerian children with Type 1 Diabetes Mellitus as determined by ultrasonography using the carotid, femoral and brachial arteries. Method: A prospective observational study was performed on all 10 children diagnosed with diabetes mellitus at the paediatric endocrinology clinic, in a tertiary unit based in Nigeria over a six-month period. Results: All 10 children were aged between 12 - 17 years (Median = 16 years) and consist of 5 (50%) males and 5 (50%) female. The duration of diabetes ranged from 0.2 to 9 years. Four (40%) of the subjects had thickened carotid intima media thickness on either the left or right common carotid artery; 5 (50%) had 0% flow mediated dilation of the brachial artery while the remaining 5 (50%) had normal flow mediated dilation; while 2 (30%) had intima media thickening of either the left or right superficial femoral artery using a cut-off value of 0.9 cm. Conclusion: Children with Type 1 Diabetes Mellitus have ultrasonic evidence of ongoing atherosclerosis. The use of ultrasound is recommended for detection and monitoring of atherosclerotic changes in children with DM.