Dilatation of the upper urinary tract occurs in more than 80% of pregnant women during the last half of pregnancy. It is caused by compression of the ureter between the growing uterus and linea terminalis. A few patients develop pathological dilatation, flank pain and impaired renal function, a so-called symptomatic hydronephrosis. We have treated ten patients by means of internal drainage by using double pigtail catheters. Nine patients were completely relieved of their symptoms, and one reported marked reduction of pain. Five women complained of irritation of the bladder. In three of the women the intravesical portion of the catheter was shortened with success. Eight women kept the stent up to the time of birth. Two were removed two and eight weeks before delivery because of infection. There were no serious complications. Use of double pigtail catheters is a safe and simple way of treating symptomatic hydronephrosis of pregnancy.