Lithium is among the most used medications in the treatment of bipolar disorder, in preventing depressive and manic episodes, as well as reducing the risk of suicide in the population with this disorder.We report a case where the endocrine dysfunction of hypothyroidism and hyperparathyroidism were diagnosed in parallel.The 54-year-old female patient was treated for bipolar disorder with Lithium for more than 18 years. For 17 years, she had not been subjected to other biochemical controls. Recently the patient complained of fatigue, dizziness, and headache.. Due to the long-term use of lithium, she was asked to measure her level of lithium in the blood, which resulted in hight level 3.23 mEq/L. Biochemical balance, which resulted in TSH 37 mIU/L and PTH 126 pg/mL. In patients with long-term treatment with Lithium, the function of the thyroid gland, parathyroid gland and calcium metabolism should be periodically monitored .