This paper describes a group of female patients admitted to mental hospital who in the past had undergone thyroidectomy for thyrotoxicosis. It was thought that a group of this kind who had been admitted might show, possibly in an exaggerated form, the personality features said to be common to individuals predisposed to thyrotoxicosis. The series does not include any toxic psychosis attributable to the disease itself and the title may possibly be misleading in this respect. Most psychiatric studies have dealt with the patient at the time of the illness and the emphasis has tended to be on precipitating factors. A much quoted study is that of Conrad (1) (1934). As a psychiatrist working in a thyroid clinic she described 57 cases referred for psychiatric opinion and used 48 cases not so referred as controls. She concluded from a careful study that the onset of the illness was due to two main patterns of emotional disturbance: (1) fear of loss of shelter and affection equivalent to deprivation of mother, (2) fear of dangers of the mother role. She found a large number of cases where there had been loss of the mother at an early age. Ham, Alexander and Carmichael (1951) (2) remind us that the disease occurs spontaneously only in man, not animals, and rarely in primitive communities. They describe a “specific dynamic pattern” in thyrotoxicosis, viz., Frustration of dependent longings and persistent threat to security (exposure to death and other threatening experiences in early life, causing unsuccessful premature attempts to identify with the object of the dependent cravings. There is a continued effort toward premature self sufficiency and to help others. These strivings for self sufficiency and taking care of others fail causing thyrotoxicosis. Lidz and Whitehorn (1949) (3) also regard thyrotoxicosis as following in almost every case a somewhat similar pattern. They regard these patients as a group less wanted than their sibs but eventually achieving parental affection by being “good children” (in the exaggerated sense) and persist in this pattern of behaviour in adult life. They expect the same unswerving fidelity they gave to their parents in return for excess of affection that they give to a parental figure. These authors claim that this almost invariable pattern provides short cuts in therapy, e.g., when the illness arises soon after marriage, problems are apt to revolve about difficulties in leaving the parental home. Working on different and more objective lines Ruesch (4) and his colleagues at the Thyroid Clinic of the University of California studied 43 patients carefully selected to give a fair representation of patients treated by thyroidectomy. They verified thyrotoxicosis by histological reports on the excised portion of the gland. Each patient had 5 interviews and abbreviated Wechsler and Minnesota Multiphasic Personality Inventory Tests. Their main interest was the prolonged psychological invalidism which had been noted to immediately follow operation. They found that patients with delayed recovery tended to have a long record of previous hospitalization, and a high frequency of major and minor operations. In the M.M.P.I. the most common pattern was “undifferentiated normal”. They concluded that patients with thyroid disease are not entirely normal sociopsychologically, but the group could be subdivided into two entities: (1) normal or almost normal, (2) hysterical or anxious type in female patients, or dependent personalities in male patients.