Background Some studies have described the relationship between autoimmune diabetes or type 1 diabetes mellitus (T1DM) and vitamin D deficiency. Few studies correlate between vitamin D deficiency and glycemic control. Purpose This study was conducted to appraise the status of vitamin D in adolescent and young adult T1DM patients and to correlate its deficiency to glycated hemoglobin (HbA1c). Patients and methods Around 63 Kuwaiti patients with T1DM were recruited in a descriptive crosssectional study in April 2015. Serum level of vitamin D [25(OH)D] was measured using enzyme-linked immunosorbent assay, and glycemic control was measured by HbA1c using autoanalyzer. The relationship between vitamin D levels and HbA1c was analyzed by Spearman’s correlation. Among the participants, 21 (33.3%) were male and 42 (66.7%) were female. The mean age was 18.41±6.19, and the mean diabetes duration was 6.98±4.99. The mean vitamin D concentration was 47.29±2.91 nmol/l, with 38.1% of participants identified to have vitamin D deficiency and 19% identified to have vitamin D insufficiency. There were high levels of HbA1c (10.08±2.28), with a significant inverse correlation between HbA1c and vitamin D (r=−0.374 and P=0.003). Conclusion Low vitamin D in T1DM is extremely highly and closely correlated to HbA1c. We recommend that evaluation of the level of vitamin D in type 1 diabetic patients is very critical, and vitamin D supplementation may improve glycemic control.