The purpose of this study was to determine the position, appearance and dimensions of the abomasum of 50 healthy 4 cows by ultrasonography. The ventral abdominal region caudal to the xiphoid process was examined with a 3.5 MHz linear 5 transducer. The abomasum could be visualised from both sides 2 and from the ventral midline of 47 of the cows. The abomasum could be clearly differentiated from adjacent organs because of its contents, which appeared as a heterogeneous, moderately echogenic structure with echogenic stippling. However, the wall of the abomasum appeared, if at all, as a narrow echogenic line. Parts of the abomasal folds were visible occasionally as echogenic structures within the abomasum. Slow movement of the feed in the abomasum was also often visualised. The pylorus was positively identified in only one cow. The cranial margin of the abomasum was situated up to 15 cm caudal to the xiphoid process. The abomasum was between 7.4 and 42.9 cm long, and its maximal extent, measured from the ventral midline to the left, was from 5.0 to 26.0 cm in the cranial region and from 5.0 to 16.0 cm in the caudal region. From the ventral midline to the (b) right, it was from 5.0 to 33.0 cm in the cranial region and from 28.0 to 36.0 cm in the caudal region. The minimal dorsoventral 5, dimension of the abomasum ranged from 0.7 to 7.2 cm, and its maximal dorsoventral dimension ranged from 3.6 to 11.1 cm.