Background: A hydatidiform mole or molar pregnancy is the most prevalent gestational trophoblastic disease (GTD). About 55%-60% of women with trophoblastic diseases have overt hyperthyroidism at the time of diagnosis, which may have severe manifestations. This study examined the relationship between gestational hypertension and the level of thyroid hormones with beta human chorionic gonadotropin (β-HCG) in patients with a hydatidiform mole. Materials and Methods: This cross-sectional study enrolled 65 patients with a hydatidiform mole admitted to Khalij-e Fars hospital, Bandar Abbas, Iran. Patients were divided into three groups of clinical hyperthyroidism, subclinical hyperthyroidism, and healthy. The serum levels of thyroid-stimulating hormone (TSH), T4, T3, and β-HCG were checked in all subjects, and the relationship between gestational hypertension and the level of thyroid hormones with β-HCG in patients with a hydatidiform mole was examined. Results: The mean age of patients was 29.93 ± 9.04 years, and their mean gestational age was 11.09 ± 4.2 weeks. In this study, 12.3% of the patients had subclinical hyperthyroidism, 41.5% had clinical hyperthyroidism, and 46.2% were healthy. A significant relationship was found between the serum level of β-HCG and thyroid function in patients with clinical and subclinical hyperthyroidism compared to the healthy group (P= 0.001). No significant relationship was found between systolic/ diastolic blood pressure and the serum level of β-HCG. Conclusion: A significant relationship was observed between the serum levels of β-HCG and TSH, free T3, and free T4 in patients with a hydatidiform mole and thyrotoxicosis. Thus, early diagnosis of hyperthyroidism can help treat these patients more quickly.