Background and aim: Childhood obesity is associated with an increased risk of chronic disease. We aimed to determine the association between vitamin D defi ciency and cardiovascular risks in obese children. Method: The studied children were selected from obese children who were followed up at obesity clinic, aged 6-17 years. Basic demographic information and laboratory data were collected retrospectively from hospital records. Results: A total of 310 students (178 [57.4%] girls) were evaluated for 25-hydroxyvitamin D (25[OH] D) levels in late winter/spring. The prevalence rates of vitamin D defi ciency, insuffi ciency, and suffi ciency were 62.3%, 34.5%, and 3.2%, respectively. Insulin resistance was observed in 146 (47.1%) children; the frequencies of dyslipidemia and hypertension were 31% and 19.4%, respectively. The mean atherogenic dyslipidemia ratio was higher in the defi cient group (p = 0.049). Inverse correlations of 25(OH) D levels were observed with homeostasis model assessment of insulin resistance values (r = -0.146, p = 0.010). The mean values of 25(OH) D (ng/mL) were lower in girls (12.15 ± 6.60) than in boys (16.48 ± 8.69) (p < 0.05) and in children with hypertension (11.92 ± 5.48) than in those without (14.50 ± 8.24) (p < 0.05). Conclusions: Vitamin D defi ciency is observed more frequently than expected in obese children and adolescents. Our fi ndings indicate that low 25(OH) D levels are associated with insulin resistance. Vitamin D defi ciency could contribute to the morbidities associated with childhood obesity, such as insulin resistance or diabetes mellitus, increased cardiovascular/cardiometabolic risks, atherogenic dyslipidemia, and hypertension.