The aim of this study is to document the impact of thyroid hormones on the autonomic nervous system (ANS), expressed by heart rate variability (HRV) and heart rate turbulence (HRT), in patients with hyperthyroidism, compared to controls. Another purpose is to determine if HRV and HRT parameters are significantly correlated with the levels of thyroid hormones and the duration of hyperthyroidism. We studied HRV, in time and frequency domain, and HRT in a group of 113 premenopausal women, with still untreated overt hyperthyroidism, without cardiovascular diseases or risk factors for atherosclerosis, admitted between 2015 and 2018 in the Endocrinology Clinic of our hospital and compared the results with data obtained in 29 healthy controls. Depending on the severity and duration of hyperthyroidism and levels of thyroid hormones, patients were assigned to three groups: mild and moderate hyperthyroidism, severe and recurrent forms. We performed 24 hours Holter monitoring in patients and controls. Regarding HRV parameters in time domain, they were significantly depressed in patients comparing to controls. Referring to HRT, all patients had abnormal, positive values of turbulence onset (TO) and we documented statistically significant differences (p[0.001) when compared to controls. All patients had normal positive values of turbulence slope (TS), which decreased parallel with the severity of hyperthyroidism. In patients with hyperthyroidism, we documented depressed values of HRV parameters in time domain, correlated with the duration and severity of the thyroid disease. Our patients had pathologic values of TO. Although positive, TS values were lower when compared to controls.