Necrotizing funisitis (NF) is a distinctive inflammatory condition of the umbilical cord, characterized by perivascular concentric rings of inflammatory cells, necrotic debris, or calcium deposits. Necrotizing funisitis has been strongly associated with syphilis by some investigators, while others have failed to link NF with any consistent infectious agents. We examined 45 cases of NF to determine its relationship with syphilis. Five (11%) mothers had syphilis as confirmed by a positive rapid plasma reagin test and a positive fluorescent antibody absorbed test, 31 (69%) had a negative rapid plasma reagin test or venereal disease research laboratory test, and test results were not available for the remaining nine (20%). There was no record of syphilis in those babies born to mothers without confirmed syphilis. Estimated gestational age at the time of delivery ranged from 18 to 40 weeks (mean, 28 weeks). Prolonged rupture of membranes was present in 28 (62%) of the mothers, and ranged from 1 to 51 days (mean, 9 days); this was the most frequently seen maternal factor in connection with NF. Fourteen (31%) of the babies were stillborn or nonviable, including three (60%) of the five born to mothers with syphilis. Maternal and fetal cultures revealed no consistent microorganisms. Placental histology was significant for chronic villitis in 26 (58%) cases, including all five (100%) with maternal syphilis. Acute chorioamnionitis was present in each case (100%) and varied from mild to severe. We conclude that (1) NF has a polymicrobial etiology, (2) in the absence of other placental findings associated with syphilis NF should not be considered presumptive of this disease, and (3) factors leading to NF may also contribute to acute chorioamnionitis, premature rupture of membranes, and stillbirth.