Over the past 30 years, prenatal corticosteroid treatment, called betamethasone has been administered to thousands of women at risk of premature birth to accelerate fetal lung maturation in the preterm neonates. A remarkably higher survival-rate of premature and infants with very low birth-weight, highlights the efficiency of this treatment. However, the long term effects have not been analyzed in detail, especially the possible effects on the immune system. This is very important to know considering that other steroids are known to induce cell death of developing T cells.