In adults, low levels of vitamin D are associated with hypertension. The aim of this study was to evaluate the relationship between 24-h blood pressure (BP) patterns and vitamin D levels in obese children. We recorded anthropometric parameters, took blood samples for 25-hydroxivitamin D measurements and monitored ambulatory BP (ABP) in 32 obese children (male/female: 21/11, age 7-16 years). Subjects in the lower tertiles had higher homeostasis model assessment of insulin resistance, nighttime systolic and diastolic ABP, nighttime systolic and diastolic ABP load, 24-h ABP index and nighttime systolic and diastolic ABP index than those in the higher tertile. Vitamin D correlated negatively with 24-h and nighttime systolic ABP, 24-h systolic ABP load, nighttime systolic and diastolic ABP load, 24-h systolic ABP index and nighttime systolic ABP index. The percentage of subjects with pathological 24-h systolic BP (SBP) load, nighttime SBP load, nighttime diastolic BP (DBP) load, nighttime SBP index and nighttime DBP index increased progressively as the vitamin deficiency categories increased (χ(2)=10.26, P<0.05; χ(2)=16.34, P<0.01; χ(2)=10.23, P<0.05; χ(2)=10.38 and χ(2)=10.06, P <0.01). Low levels of vitamin D in obese children were associated with a higher BP burden, especially at night.