Alterations in blood pressure in attention-deficit/hyperactivity disorder (ADHD), specifically during dopaminergic stimulant intake, are not fully understood. It has been reported that vitamin D deficiency might modify dopaminergic pathways and thus influence ADHD symptoms. Using data from the nationwide German Health Interview and Examination Survey for Children and Adolescents (KiGGS) study, we compared blood pressure and vitamin D levels in healthy controls to both diagnosed ADHD patients and suspected ADHD subjects, as defined by a value of >/=7 on the hyperactivity-inattention subscale of the Strengths and Difficulties Questionnaire. In a total cohort of n = 6922 study participants aged 11-17 years, mean arterial blood pressure was significantly higher in controls (86.7 +/- 8.2 mmHg) than in the two groups of confirmed (85.5 +/- 7.8 mmHg, p = 0.004, n = 430) and suspected ADHD patients (84.6 +/- 8.2, p < 0.001, n = 399). In addition, we found an inverse association between vitamin D and blood pressure in both ADHD groups (p < 0.003). Regression analyses adjusted for age, sex, body-mass index, psychotropic medication use, and serum vitamin D levels confirmed that low blood pressure was a significant and independent predictor of ADHD. Furthermore, we observed that vitamin D mediated the effect of systolic blood pressure on ADHD diagnosis (b = 0.007, 95 % confidence interval [CI] 0.001-0.013, p = 0.021, R 2 = 0.050). In a large and representative national sample of German adolescents, we found a significant association between low blood pressure and ADHD symptoms. In addition, we observed that circulating vitamin D mediated the inverse relation between blood pressure and ADHD, although the effect size was very low. These findings highlight the role of dysregulated pathways of the autonomic nervous system in ADHD.