A full-term newborn developed oliguric renal failure at 24 hr of life, which persisted for several days. Her mother ingested therapeutic doses of nimesulide, a non-steroidal anti-inflammatory (cyclo-oxygenase-2 inhibitor) drug, during the last 2 weeks of pregnancy. She was found at delivery to have developed oligohydramnion, esophagitis, and a bleeding peptic ulcer. The infant's fractional excretion of sodium was very low (0.5%) pointing for a severe vasoconstrictive mechanism involved. Renal sonogram showed hyperechogenic medullary papillae, which resolved during convalescence. This case emphasizes the importance of renal prostagandins in the control of vascular tone and sodium homeostasis. This is the first report of an adverse effect of fetal renal circulation by maternal ingestion of nimesulide.