Various dimensions of normal brain stem were measured on T1-weighted mid-sagittal magnetic resonance(MR)images in 103 Korean adult to provide criteria for detecting brainstem abnormallity. Five measurements were made:(A) the distance between interpeduncular fissure and aqueduct, (B) the distance from anterior surface of cerebralpeduncles to aqueduct, (C) the distance between anterior surface of the pons midway to fourth ventricular floor,(D) the shortest anteroposterior diameter of the medulla at pontomedullary junction, and (E) the shortest anteroposterior diameter of the medulla at medullospinal junction. The mean distances for A, B, C, D, and E were 0.4, 10.7, 22.8, 13.3, 9.4mm, respectively. There was no statistical difference of each dimension between male andfemale, and among different ages.