Mutations of the PROP-1 gene cause combined pituitary hormone deficiency. Progressive ACTH/cortisol insufficiency is found in a few patients. Congenital hypoplasia of the anterior pituitary gland is the most common magnetic resonance imaging finding in patients with PROP-1 mutations. We present two brothers with compound heterozygosity for the two mutations 150delA and 301–302delAG of the PROP-1 gene. Both showed combined pituitary hormone deficiency of GH, TSH, PRL, and gonadotropins, as is typical for PROP-1 deficiency. We observed a developing insufficiency of ACTH and cortisol secretory capacity in both patients. Computed tomography revealed an enlarged pituitary in the older brother at 3.5 yr of age. Repeated magnetic resonance imaging after 12 yr showed a constant hypoplasia of the anterior pituitary lobe. Similarly, magnetic resonance imaging of the younger brother showed a constant enlargement of the anterior pituitary gland until 10 yr. At the age of 11 yr, the anterior pituitary was hypoplastic. The reason for pituitary enlargement in early childhood with subsequent decrease in pituitary size is not known. We speculate that altered expression of early transcription factors could be involved. Because both patients have the same PROP-1 mutations and an identical pattern of combined pituitary hormone deficiency, we suggest that early pituitary enlargement may be the typical course in such patients in whom pituitary surgery is not indicated.