We report a young adult female case of Wilson's disease presenting with mental disorder and frontal lobe signs. The patient was admitted to our neurological unit on October 4, 1999 because of schizophrenia-like symptom, dysphagia, dysarthria and gait disturbance. She showed slowly progressive rigidity and dystonia. Her parents were the second cousins. Neurological examination revealed bilateral pyramidal and extrapyramidal signs, frontal lobe signs (include the imitation behavior). Tendon reflexes were slightly exaggerated in all extremities. Bilateral Babinski, Chaddock and Hoffmann signs were positive. Her verbal IQ on the Wechsler Adult Intelligence Scale-revised was 49. Biochemical examination revealed low plasma copper and ceruloplasmin concentration. Cerebrospinal fluid was normal. Cranial MRI demonstrated diffuse brain atrophy and enlargement of the lateral ventricles. T2-weighted images of the MRI demonstrated hyperintense signal in both thalamus and basal ganglia. SPECT showed hypoperfusion in the left frontal lobe, both thalamus and basal ganglia. EEG revealed diffuse theta wave. The diagnosis of Wilson's disease was made and the treatment of D-penicillamine 900 mg per day was started. This hypoperfusion of SPECT and EEG findings improved after 2 months under D-penicillamine therapy. Neurological findings showed slight improvement. A few Wilson's disease patients presenting with mental disorder have been reported. Wilson's disease should always be considered in differential diagnosis of mental disorders. We emphasize the importance of early diagnosis and treatment of Wilson's disease.