A classification of the changes seen in the placentas of nondiabetic, non-high-risk obstetrical patients, and its relationship to fetal pulmonary maturity, has been the subject of two recent reports. Successful (100 per cent) correlation has been concluded from these studies when a Grade III placenta has been demonstrated in gestations of 33 weeks to term. To determine whether the same high degree of reliability would hold for the diabetic and high-risk obstetrical patient, 78 such patients were analyzed. All except one delivered at 33 weeks to term, and all had amniotic fluid lecithin-sphingomyelin (L/S) ratio determinations within 48 hours of sonographic placental grading and within seven days of delivery. Of the Grade III placentas (n = 13), 23 per cent had "immature" L/S ratios. However, there was no case of infantile respiratory distress syndrome (IRDS) in infants of patients with Grade III placentas. These findings suggest that placental grading may need to be part of a multifactorial assessment of fetal maturity in the diabetic or high-risk pregnancy.