Graves disease is ail autoimmune and multifactorial disease of the thyroid gland and one of the commonest reasons of the hyperthyroidism. Most of the Graves disease patients show typical symptoms of the disease such as fatique, irritability, weight loss, palpitations and heat intolerance. Mental abnormalities are also known to be present in case of Graves thyrotoxicosis. These mental abnormalities are composed of irritability, emotional lability, anxiety, depression, mania, and psychotic manifestations with paranoid and persecutive delusions. Here we presented a 38 year old woman having Graves thyrotoxicosis who had no psychiatric disorder or a history of any medical illness before Graves thyrotoxicosis but whenever the disease had started acutely patient presented some psychotic symptoms such as hallucinations, paranoid and persecutive delusions, a state of confusion, agitation and hyperactivity. In the first thyroid function test (TFT) blood thyroid hormone levels were found as follows: free T(3) (FT(3))= 8.07 pg/ml (normal value: 1.71-3.71), free T(4) (FT(4))= 1.46 ng/dL (normal value: 0.70-1.48) and TSH<0.0008 (normal value: 0.35-4.94). Patient was diagnosed as Graves thyrotoxicosis after the results of her past history, physical examination, laboratory and clinical findings and patient was given antithyroid treatment. Additionally patient was also given antipsychotic treatment to control her psychotic symptoms. After the treatment psychotic and clinical symptoms of the patient relieved significantly. The case presented here showed that Graves thyrotoxicosis may start with acute psychotic symptoms and this condition may frequently be misdiagnosed with major psychiatric disorders. So, in the presence of the clinical cases which starts with acute psychotic symptoms, it is very important to get detailed medical and psychiatric past history, to make carefull physical examination and to make detailed medical investigations including thyroid function tests.