OBJECTIVE POTS is a heterogeneous disorder of the autonomic nervous system that can result from multiple etiologies. An increased prevalence of vitamin B12, vitamin D 25-OH and iron deficiencies has been observed in patients with POTS. This study examined the prevalence of vitamin B1 deficiency and assessed response to vitamin B1 supplementation in the deficient POTS patients. METHODS AND RESULTS Medical records of 65 consecutive patients with POTS evaluated at our clinic were reviewed. In this cohort (mean age 32, range 13-54 years; 89% female), 6% had vitamin B1 deficiency, and one of four deficient patients experienced significant improvement of POTS after oral vitamin B1 supplementation. CONCLUSION A small subset of patients with POTS may have vitamin B1 deficiency. Testing for vitamin B1 deficiency and correcting the deficiency is recommended.