Summary 1.Of an unselected group of 481 pregnant patients, 4.5 per cent had bacteriuria confirmed on two examinations: it was demonstrated in half of these to be present in both early and late pregnancy. 2.Clinical urinary infection in pregnancy occurred with greater than usual frequency in patients with previously detected bacteriuria. Six patients, or 1 per cent of the total group, had infection without previous bacteriuria. 3.Bacteriuria was demonstrated with greatest frequency in patients with abnormal glucose tolerance, with previous urinary infection, in those over 30 years old, in multiparas, and in Negro patients. 4.All but a few cases of postpartum urinary infection, as well as asymptomatic bacteriuria, occurred in patients who had shown infection prior to delivery or who had been catheterized.