This study is based on a group of more than 400 cases of disease of the urinary tract associated with pregnancy, which have been treated by one or both of us over a period of years, extending from 1919 to the present time. Many of these patients were seen in but a single pregnancy; others have been regular customers at our clinic, and we have been able to compile data covering the complete child-bearing period in a considerable group. Unfortunately, owing to various handicaps that existed in former years, the earlier observations are less complete than those made in later years. Careful selections have been made from these cases, and we have used only proved facts, suffering the necessary shrinkage in numbers in the interest of greater accuracy. A conception of the importance of urinary tract infection in relation to the whole child-bearing period in women is obviously of more