The use of PTH values of the internal jugular veins has proven to be an increasingly used tool for parathyroid surgeries, whether for patients with or without localizatory exams, but still with conflicting results regarding the reliability of the method.10, 11, 15 The present study demonstrated that there is a difference in the concentration of PTH values of the internal jugular veins in relation to adenoma laterality in patients with PHPT, in addition to obtaining a possible cutoff value in the concentration difference between the jugular veins. Here, PTH is linked to adenoma.