Thyroid diseases may lead to occurrence of psychiatric symptoms and psychiatric disorders. Hypothyroidism is a condition, which is often seen during clinical practice, and the condition is associated with various clinical pictures. Hypothyroidism is often associated with psychiatric symptoms. Anxiety, apathy, cognitive disorder and depression are commonly observed, but psychosis and mania are rare. This case report will present a patient with psychosis resulting from hypothyroidism. This case addresses a 56-years old female patient, who had diagnosis of hypothyroidism 4 years ago and has had psychotic symptoms for 6 months. Patient was referred by relatives to our outpatient clinic due to complaints of insomnia, auditory hallucinations and abnormal thoughts (her husband is cheating her and she is bewitched) and talking to herself. On psychiatric assessment, it was found that her self-care was poor. Periorbital edema was noted. Skin was dry and hair was not tidy. Patient had an apathic appearance. Orientation was intact. Affect was inappropriate. Mood was irritable. Thought content indicated mystic, jalusic and persecutory delusions. On blood analyses, T3 and T4 were low, while TSH and thyroid auto-antibodies were high. Personal history indicated that diagnosis of hypothyroidism was made 4 years ago, but patient had poor compliance and she did not regularly return for control visits. Familial history indicated no specific finding. Most possible diagnosis was hypothyroidism-induced psychosis and patient was started on hormone replacement therapy and risperidone (1 mg/day). Self-care improved and delusions regressed. Psychotic and cognitive symptoms completely disappeared 1 week after thyroid parameters were restored to normal range. Psychotic symptoms occurred when clinical picture of hypothyroidism enhanced; on the contrary, complaints regressed when the patient had euthyroid status. Late onset of psychotic picture and absence of psychosis in personal and familial histories further support the possibility that psychosis is secondary to overall state of health. Thyroid diseases may lead to a wide spectrum of psychiatric disorders. Therefore, thyroid function tests should be routinely ordered for psychiatric patients.