Recently, perinatal outcome in patients undergoing chronic hemodialysis has been improved. But the conditions that will most likely result in successful pregnancy are still obscure. We retrospectively analyzed 15 pregnant patients who were undergoing chronic hemodialysis before pregnancy treated in our perinatal center. We divided these 15 cases into 2 groups: one group of 11 patients whose infants survived and the other group of 4 patients whose infants died 6 h to 8 months after birth due to prematurity. The rate of successful pregnancies having a surviving infant was 73.3% (11/15). We compared the maternal conditions and the progress of pregnancy in the 2 groups. Significant differences (p<0.01) were seen as follows. The patients in the group whose infants survived underwent hemodialysis for a shorter term before pregnancy (1-6 years), most of them (9/11) could produce urine (> or =50 ml/day), and the period of gestation was extended (33.3+/-4.7 weeks), so the infants were heavier (1,782.9+/-678.3 g). All the patients who underwent more than 9 years of hemodialysis could not have a surviving infant. From this we can assume that the shorter the period of dialysis before pregnancy, the better the condition is that is likely to result in women giving birth and the better is their infant's chance of survival.