Over a period from September, 1965, to November, 1967, left displacement of the abomasum was observed in 17 Holstein-Friesian cows, 16 of which were patients from 3 towns adjacent to the University Farm, which is located 60 miles northeast of Tokyo. There was nothing noticeable in diet and circumstances that might have been predisposing factors in these cows. there was no apparent seasonal relationship to the development of the disease.The onset of symptoms was approximately 11 weeks to 1 day ante-partum in 7 cases, immediately following parturition in 2 cases and 1 to 41 days postpartum in 8 cases.Simultaneous auscultation and percussion was proved to be the most rapid and reliable method of diagnosis. A high-pitched resonant ping sound was heard in all cases when percussion was done on the last ribs with the percussion hammer. In 6 cases, endoscopy via the left paralumbar fossa was attempted and resulted in confirmation of displacement.Bilateral flank approach associated with omentopexy to the right abdominal wall was used for the treatment of 12 cows in the standing position. Right paramedian approach with omentopexy to the ventral abdominal wall was performed in 4 cases. Twelve of 16 cases recovered uneventfully. Of those 12 cows, one calved twice and four once subsequent to surgery; seven were pregnant and three not pregnant at the end of November, 1967; two were sold. Four cows were destroyed after surgery because of complications, such as disseminated pulmonary abscesses originated from a piece of wire perforating the esophagus, adhesion of the abomasum with the left ruminal wall, aggravated suppurative mastitis, and displacement of the dilated abomasum to the right flank following devouring of a sheet of blanket.In the remaining one cow, in which omentopexy had not been performed on account of spontaneous replacement of the displaced organ, the condition relapsed 18 days later. Then the cow was subjected to surgical correction by practitioners.