Data were gathered on 25 pregnancies in 23 women with moderate renal insufficiency as defined by a serum creatinine level of 1.4 mg/dl or greater prior to or at the onset of pregnancy. Twelve of the women had primary glomerular diseases, five (accounting for seven pregnancies) had interstitial diseases, and six had other renal diseases. In seven women with baseline serum creatinine levels ranging from 1.7 to 2.7 mg/dl, pregnancy was accompanied by a decline in renal function that was believed to be greater than expected from the natural history of the disease. The change ranged from a rise in serum creatinine level of 1.2 mg/dl to a functional decline that required dialysis. In 14 women (16 pregnancies), renal function either remained stable or declined to a degree consistent with the natural history of the disease. In two, the follow-up period was not long enough to judge the effect on the natural history of the disease. In 14 pregnancies, development or worsening of hypertension occurred. In nine, the diastolic blood pressure rose to 110 mm Hg or greater, and delivery was required because of hypertension. Twenty-three of 25 pregnancies ended in live births (92 percent) and 21 babies survived (84 percent). Fourteen of the 23 live births were premature. It is concluded that, in a substantial fraction of women with moderate renal insufficiency, pregnancy is accompanied by a decline in renal function; however, the fetal survival is much better than previously reported.