To study the diagnostic and therapeutic features of pituitary tumorous hyperplasia due to primary hypothyroidism. Fifteen patients with pituitary tumorous hyperplasia were studied in clinical manifestation, pathologic, endocrinological, radiographic and therapeutic features retrospectively. All of these patients suffered from primary hypothyroidism. Magnetic resonance imaging (MRI) scanning found that there were masses in the sellar region with equal T1 and little longer T2 signal, and which could be obviously enhanced by gadolinium EDTA injection. Diameters of these masses were between 1.1 and 2.5 cm. Thyroxine substitution therapy was ordered. Four months later, MRI scanning found that the masses disappeared and only normal pituitary gland left. Plasma thyroxine, thyroid-stimulating hormone (TSH), and prolactin (PRL) levels dropped to their normal ranges. Thyroxine substitution therapy was the first choice of pituitary tumorous hyperplasia due to primary hypothyroidism. If they are followed by TSH adenoma, or the optic chiasma was pressed by the enlarged pituitary, transsphenoidal microsurgery could be applied.