Magnetic Resonance (MR) imaging was carried out on 33 patients with idiopathic growth hormone deficiency, in 22 of whom CT scan had been carried-out previously. Twenty-one patients presented some complications at birth. Both MR and CT were positive in the evaluation of the sella. MR imaging exhibited a higher degree of accuracy than CT in the evaluation of pituitary gland, pituitary stalk and brain anomalies. On the basis of pituitary morphology demonstrated by MR imaging, and perinatal histories, a classification is proposed which divides our patients into three group: A) a first group of 13 patients presenting severe hypoplasia of the anterior pituitary lobe, hypoplasia of the stalk and ectopia of posterior lobe. The underlying cause of these anatomic defects might be developmental in origin, and date from early intrauterine life, probably worsened at birth. B) a second group of 10 patients presenting severe hypoplasia of the anterior pituitary lobe. A perinatal event and birth trauma might be responsible for pituitary damage. C) a third group of 10 patients with no morphological abnormalities of the pituitary gland. A derangement of the neuroendocrine mechanism which control the growth hormone secretion might account for these patients.