Twenty surgically proven pituitary microadenomas were examined with MR imaging and CT. MR demonstrated 20 of 20 microadenomas: 90% of the tumors were hypointense on T1-weighted images before Gd-DTPA administration and in 45% the tumors were more clearly delineated postcontrast. CT demonstrated 19 of 20 diagnosed microadenomas: showing low attenuation in 85% of the tumors precontrast. Iohexol facilitated delineation of the tumors in 45%. Focal enlargement of the gland and diaphragma sellae convexity were more useful than infundibular tilting and sellar-floor erosion as ancillary findings supporting the diagnosis. In general, CT and MR agreed regarding the microadenomas' size and location, measurement of enlarged intrasellar contents, detection of the diaphragma sellae bulge, and demonstration of infundibulum abnormality. CT was more sensitive than MR in identifying sellar-floor erosion. We suggest that CT be the first method for demonstration of microadenomas.