Background: Considerable variations in diagnosis and therapeutic practices are reported for hyperthyroidism (HT) between countries. Methods: A clinical study was conducted among a representative sample of 263 endocrinologists in France. All consecutive patients seen for HT during the study period were included. Diagnosis and treatment modalities were recorded from hyperthyroid patients with Graves disease (GD, n = 802), multinodular goiter (MNG, n = 121), and toxic adenoma (TA, n = 69). Results: Antithyroid antibodies were measured in half of the population (anti-TPO in 48.5% and anti-TSH receptor in 57.8%). Patients had thyroid ultrasonography and scintigraphy in 93.8 and 40.3%, respectively. Therapeutic management depended on the etiology: for the first episode of GD, antithyroid drugs (ATDs) were the first-line treatment in 91% of the patients, combined with surgery in 6.1% and with radioiodine in 2.9%. Surgery was preferred to radioiodine in MNG (52.6 vs. 22.4%) and TA (59.1 vs. 24.2%). Euthyroid status was achieved after 3 months in 64.4% of GD. A “block and replace” protocol was used in 41.2% of patients. After 3 months, 73% of patients were euthyroid in the “block and replace” group compared to 56.2% in the group with ATDs alone (p = 0.009). For MNG and TA, more than 75% of patients were euthyroid at the 3-month follow-up. Conclusions: Large discrepancies remain between clinical practice and international guidelines. These results should boost efforts to improve adherence to these guidelines.