We describe a 23-yr old woman with congenital combined pituitary hormone deficiency (CPHD) diagnosed at 10 years of age and a large sellar mass discovered at the age of 19 years, when her first pituitary MRI was performed. The mass (height: 13 mm) extended to the suprasellar region, close to the optic chiasm, showed signal hyperintensity in T1- and hypointensity in T2-weighted images, with no enhancement after gadolinium injection. Although these MRI features were suggestive of Rathke's cleft cyst, cystic craniopharyngioma or previous hemorrhage, no visual symptoms, diabetes insipidus and/or hyperprolactinemia were present. In addition, similar MRI findings had been previously described in a few cases of CPHD due to PROP-1 mutations, which prompted us to carry out a molecular study before any therapeutic decision was made. A 301302delAG PROP-1 mutation was found in her DNA and the patient was closely followed through ophthalmologic evaluation and pituitary MRI scans. During a 3.6-year follow-up, we were able to document a marked initial growth followed by shrinkage and recurrent growth of the PROP-1 sellar mass. The patient remains free of compressive neuro-ophthalmological signs, suggesting that surgical intervention is unnecessary in these cases. However, they must be followed closely with sellar MRIs and campimetry until the mass completely regresses.