Twelve patients with growth hormone-producing pituitary adenomas were investigated to evaluate correlations between magnetic resonance (MR) appearance and tissue characteristics, sellar expansion, suprasellar tumor extension, and tumor consistency. MR imaging could detect microadenomas with a characteristic enhancement delay of gadolinium-diethylenetriaminepenta-acetic acid in the surrounding normal pituitary gland. Macroadenomas and giant tumors appeared on T2-weighted images as mostly high intensity, while varied greatly on T1-weighted images. The signal intensities of growth hormone-producing adenomas were more homogeneous (80%) than those of other functioning and non-functioning adenomas on T1-weighted images. However, there was no typical MR imaging for the tissue characteristics of the growth hormone-producing adenomas, and no particular correlation with suprasellar extension or consistency. Postoperative MR findings showed that the transcranial approach was superior for total or subtotal removal of large tumors, especially with suprasellar extension up to the upper third ventricle. The transsphenoidal approach can achieve a satisfactory decompressive effect on the optic chiasm, but more radical removal is required to achieve a normal hormone level.