Primary hyperparathyroidism (PHPT) is the leading cause of outpatient hypercalcemia associated with increased cardiovascular risk. The flow-mediated vasodilation (FMV) has been proposed as a non-invasive method for assessing endothelial function. To compare the endothelial dysfunction measured by FMV and diastolic dysfunction in patients with PHPT before and after parathyroidectomy. We performed a quasi-experimental (before-after) study to evaluate diastolic function and FMV in patients with PHPT before and six months after parathyroidectomy. Fifteen patients completed study: 12 women and 3 men; 73% presented lithiasis, 27% osteoporosis and 53% metabolic syndrome; 73% presented diastolic dysfunction before the surgery and 60% after the surgery (p = 0.09). Post-isquemia brachial diameter improved from 41 mm (before surgery) to 46 mm (after surgery; p = 0.020). After surgery, we also observed an increase in the brachial diameter pre vs. post-ischemia from 41 to 46 mm (p = 0.005). Before surgery, the change in the delta of brachial diameter pre and post-ischemia was 1 mm and up to 4 mm after surgery (p = 0.03). There is a minor endothelial dysfunction measured by FMV in patients who underwent surgery for PHPT at 6 months after surgery, as well as a trend towards improvement in diastolic dysfunction. Echocardiography can be useful in the preoperative evaluation in patients with asymptomatic PHPT. Copyright: © 2019 Permanyer.