Background.Mother-to-child transmission of HIV has decreased in industrialized countries because of widespread use of antiretroviral therapy (ART) by HIV-infected pregnant women and perhaps to increased use of elective cesarean section. We evaluated changes in the use of ART and mode of delivery among HIV-positive pregnant women in North Carolina.Methods.We reviewed the medical records of HIV-exposed infants born in North Carolina between January 1, 1998, and December 31, 1999, who were tested for HIV DNA. These results were compared with data collected on HIV-exposed infants born from 1993 through 1997.Results.The use of combination ART increased from 1.5% in 1996 to 73% in 1999. The most common ART was zidovudine/lamivudine (39%) followed by zidovudine-lamivudine-nelfinavir (34%), although 34 combinations were used. Elective cesarean sections in the state increased significantly from 16.5% in the first half of 1998 to 49.4% in the second half of 1999. Overall transmission rates declined from 24.5% in 1993 to an average of 10.6% in 1994 to 1996 (41 of 385) and to 3.5% in 1997 to 1999 (15 of 428).Conclusions.Increased use of combination ART and elective cesarean section was accompanied by consistently low rates of perinatal transmission. However, because perinatal transmission rates were also low among women who used combination therapy and had vaginal deliveries, it is difficult to determine how much additional benefit cesarean section affords. Most HIV transmission occurred among women who lacked prenatal care and did not receive or adhere to ART.