The objective of the study was to characterize human immunodeficiency virus (HIV)-seropositive pregnant adolescents according to maternal reproductive, behavioral, and psychosocial characteristics. Data were derived from the national HIV/AIDS Reporting System (HARS, 2001-2004) and the Perinatal Guidelines Evaluation Project (PGEP, 1997-1999). Births to HIV-seropositive 13- to 21-year-olds reported to HARS via pediatric case report forms, and HIV-seropositive pregnant adolescents (aged 13- 21 years) who participated in PGEP were identified and characterized. In the 28 states with confidential, name-based perinatal HIV exposure reporting, 1183 live births occurred to 1090 seropositive adolescents. Fifteen births were to perinatally HIV-infected adolescents. HIV serostatus was known before the index pregnancy in half the cases (52.6% and 49.2% in HARS and PGEP, respectively). Of seropositive PGEP adolescents, 67% were previously pregnant; most pregnancies (83.3%) were unplanned. Many HIV-seropositive pregnant adolescents were aware of their serostatus when they became pregnant. Pregnancy and transmission risk reduction interventions targeting young seropositive females are needed.