The clinicopathologic features of 17 cases of an unusual variant of chorioamnionitis distinguished by a pure or predominantly chronic inflammatory infiltrate in the fetal membranes rather than the usual acute inflammatory reaction are reported. In six cases, there was an equal (one case) or minor (five cases) component of acute inflammation in the fetal membranes as well. Concomitant villitis, found in 11 cases, was almost uniformly lymphohistiocytic and destructive, but it varied greatly in severity. Immunoperoxidase stains for cytomegalovirus, herpes simplex I and II, and Toxoplasma gondii; Warthin-Starry, Gomori methenamine silver, Dieterle, Gram and acid fast stains; placental or amniotic fluid culture; and limited maternal serologic studies failed to identify a specific infectious etiology in any case. Seven women had experienced at least one previous spontaneous abortion, fetal death in utero, or preterm birth. No patient reported a history of fever, rash, or flu-like syndrome during pregnancy. Serious antenatal complications were numerous. Preterm birth occurred in 13 cases. Gestational age ranged from 25 to 42 weeks (mean 32 weeks) and birth weight ranged from 740 to 3,230 g (mean 2,100 g). When expressed as a percentile for gestational age, 47% of infants had a birth weight at or below the 25th percentile, and 76% were at or below the 50th percentile. Two infants were born with gross anomalies, and one infant died in the neonatal period.