It is significant that in the treatment of acute intestinal obstruction the more refined surgical procedures and the therapeutic measures that have recently been instituted to combat dehydration and to correct the accompanying alterations of the blood plasma have not had noticeable effects in lowering the mortality in this disease. This is a situation that obviously deserves thoughtful consideration by the medical profession. One method of approach to this subject is through the statistical study of results. This and the suceeding papers present an analysis of all the cases of acute mechanical obstruction (a total of three hundred and thirty-five cases) at the Massachusetts General Hospital from 1918 through 1927; cases of subacute obstruction and those due to paralytic ileus have been excluded. For the purpose of this study the cases are divided into three main groups: Group I includes all cases except those due to neoplasms (except neoplasms that