Urinary tract infections are common during pregnancy. When unrecognized, they can be responsible for complications such as threatened premature labour and impaired intra-uterine development. Detection and appropriate treatment are thus essential. This article reviews the pathophysiology of urinary tract infections during pregnancy and the three major entities involved--different but related to each other--are detailed (significant asymptomatic bacteriuria or SAB, acute cystitis and acute pyelonephritis), together with their specific treatment. SAB tends to persist during pregnancy, then leading in the absence of treatment to a potentially serious complication (acute pyelonephritis) in approximately one woman in five. SAB should be sought at the first prenatal visit by microscopic and bacteriological examination of a properly obtained urine specimen. Lower genital infections should also be sought and treated, without forgetting to remind the patient of preventive measures (adequate hygiene, sufficient urine output, post-coital micturition, regular bowel habit).