More recent studies have noted increases in ACTH and cortisol, which could result in immunosuppression. The hypogonadism observed in the presence of HIV infection is due to the general effects of chronic illness and the specific actions of drugs and infections unique to the condition. The incidence of congenital hypothyroidism has been reported to be in the region of 1 in 3600. Screening is usually carried out between the 3rd and 7th days of life. In Europe and Britain, the favoured technique is by radioimmunoassay of TSH levels on dried filter paper blood spots obtained by heel stab. It involves an extremely low recall rate for repeat tests but is unable to detect the rare case of secondary (pituitary) hypothyroidism. This disadvantage does not apply to measurement of T4 levels followed by TSH assay which is confined to specimens with low T4 values. This latter method is favoured by many American centres. Factors affecting outcome include the severity of congenital hypothyroidism, adequacy of thyroid hormone replacement in early life and the social economic background of the family. Reconfirmation of the diagnosis by interruption of treatment should be performed at 3 years of age especially in children who were diagnosed to have congenital hypothyroidism but with a thyroid gland in the normal location. Life-long treatment is required for patients with permanent congenital hypothyroidism.