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Recent studies suggest that disorders related to endocrine system, particularly thyroid diseases are the most common factor for initiating or deteriorating psychiatric complaints. Psychiatric symptoms are reported to be earliest and most significant signs and symptoms in thyroid disorders. Thyroxin addition to anti-depressant prescriptions of the patients having both hypothyroidism and depression is also recommended. Here we present a hypothyroidism case along with psychotic, cognitive and depressive disorders. Patient’s complaints rapidly improved after thyroid hormone replacement under anti-psychotic/anti-depressant therapy; however, therapy was cut upon symptoms that re-emerged after thyroid hormone replacement. A 25-year-old single male with a history of previous total thyroidectomy for papillary thyroid microcarcinoma but without any psychiatric history applied to our outpatient clinic for fatigue, anhedonia, suicidal thoughts, insomnia, seeing strange figures in people’s faces, hearing laughter, false and irrelevant inference on conversations and thoughts of harm to himself. Symptoms occured one month after surgery. Psychiatric examination showed decreased psychomotor activity, husky and slow speech, blunt affect, depressed mood, auditory perception şaws, slowed thought process, persecution delusion and suicidal thoughts. Depression with psychotic features was diagnosed and patient was admitted to inpatient service. Lab findings were as follows: free T3 was 0,58 pmol/L, free T4 was 0,14 pmol/L, and TSH was 150 mIU/L. HAM-D(The Hamilton Rating Scale for Depression) score was 31. Milnacipran 100 mg/d, risperidone 1mg/d and lorazepam 1mg/d as well as 0.15mg/d levothyroxine sodium was administered and remission was achieved. HAM-D score dropped to 5. Discontinuing thyroxin therapy caused relapse, HAM-D score increased to 21. Levothyroxine sodium administration after radioactive iodine uptake therapy improved symptoms and HAM-D score decreased to three on third day of therapy. Thyroid disorders have a wide range of neuropsychiatric disorders. Hypothyroidism may easily be ignored among these various physical and psychiatric symptoms. Therefore, routine thyroid functions screening is essential in patients presented with depression, psychosis and cognitive disorders. Underlying cause should be targeted in organic causes of psychiatric disorders. In our case; symptoms exacerbated at the end of thyroid hormone replacement therapy eventhough antidepressant/antipsychotic treatment was still being administered and improved when replacement therapy was restarted.