Diabetes mellitus (DM) is a major life-long non-communicable illness correlated with obesity and chronic undernutrition. It is particularly important to monitor the nutritional status of children with type 1 diabetes mellitus (T1DM), as they are still growing and may be affected by the disease or associated conditions like celiac disease. This study aimed to evaluate the nutritional status of children and adolescents with T1DM in Baghdad city and identify possible risk factors for undernutrition. A single-center, case-control study was conducted in Central Child’s Teaching Hospital, Baghdad, Iraq, over 9 months from November 2021 to July 2022. The study included patients with T1DM and healthy controls. Detailed history, clinical examination, and anthropometric measures were performed for all participants in the study. The mean age of the sample was 10.0 ±3.73 years and 8.68±3.1 years in diabetic patients and controls, respectively. Anthropometric measures in patients with type 1 diabetes were significantly lower than those of controls (P<0.001). All patients within the undernourished group were from large-size families compared with 75.76% of the normally nourished group, with a significant difference. The mean age of disease onset in the normal nourished group was 6.61 ± 2.78 years which was significantly earlier than that of the undernourished group (8.83 ± 2.89). Weight-for-age and BMI z-score had a significant negative correlation with HbA1c (r=-0.312, p=0.004, and r=-0.295, p=0.006, respectively). Patients with T1DM had significantly lower anthropometric measures than the normal population. Older children, female gender, large family size, and disease duration are independent predictors of undernutrition in T1DM. BMI and weight-for-age have a significant negative correlation with metabolic control of diabetes represented by HbA1c.