Hypertension is strongly predicted by the combination of low birthweight and a large placenta. This association could be due to increased fetal exposure to maternal glucocorticoids. Fetal protection is normally effected by placental 11 β-hydroxysteroid dehydrogenase (11 β-OHSD), which converts physiological glucocorticoids to inactive products. We found that rat placental 11 β-OHSD activity correlated positively with term fetal weight and negatively with placental weight. Offspring of rats treated during pregnancy with dexamethasone (which is not metabolised by 11 β-OHSD) had lower birthweights and higher blood pressure when adult than did offspring of control rats. Increased fetal glucocorticoid exposure secondary to attenuated placental 11 β-OHSD activity may link low birthweight and high placental weight with hypertension.