PURPOSE: To evaluate the significance of T2-weighted MR imaging(T2WI) in the diagnosis of pituitarymicroadenoma. MATERIAL AND METHODS: We retrospectively evaluated the MR imaging findings of 30 cases of pituitarymicroadenoma. Diagnosis was made on the basis of surgery, serum hormonal level, and the presence of mass lesion onMR (T1WI and T2WI), and conventional as well as dynamic contrast enhanced T1WI images were obtained. In each MRsequence, signal intensity and detectability of the tumor were evaluated. We also determined whether diagnosis waspossible on both T1WI and T2WI. In eight cases, histopathologic findings (cellularity, fibrosis, and cysticchange) were correlated with T2 signal intensity of the tumor. RESULTS: T2WI, T1WI, and dynamic and conventionalenhanced T1WI detected the tumor in 21 cases (70%), 21 cases (70%), 28 cases (93.3%), and 22 cases (73.3%),respectively. On T2WI, pituitary microadenomas showed a high signal in 18 cases (60%), an iso-signal in nine(30%), and a low signal in three (10%) compared with normal pituitary gland. In 20 cases (66.7%), diagnosis ofpituitary microadenoma was possible on both T1WI and T2WI, but in one case, the tumor was detected only on T2WI.Three cases with fibrosis, as seen on histopathologic examination showed an iso or low signal on T2WI. CONCLUSION: T2WI is useful in the diagnosis of pituitary microadenoma Decreased signal intensity on T2WI may suggestfibrosis.