The transformation of the human immunodeficiency virus (HIV) epidemic over the last 20 years has been remarkable. With access to appropriate therapies, clinicians can now offer infected women a much improved prognosis as well as a very high likelihood of birthing children who will be HIV uninfected. However, these advances are purchased through the use of complicated, expensive medical regimens (highly active antiretroviral therapy) that are associated with a litany of toxicities and risks. In caring for HIV-infected pregnant women and prescribing these medications, obstetricians must always bear in mind their dual responsibilities, providing optimal care to the mother and reducing the likelihood of mother-to-child transmission of HIV. To accomplish those goals, the physician must first monitor the patient's immunological and virological status including resistance testing. The results of those tests will guide the clinician in choosing when to initiate therapy and in deciding whether to use regimens directed solely at transmission interruption or those that will simultaneously treat the mother's infection. When using highly active antiretroviral therapy, physicians must be cognizant of the pregnancy-specific risks associated with some of the component agents. The core goal of all medical therapy is to bring the patient's viral load to an undetectable level. When that goal is reached, the chance of transmission to the child is minimized, the need for a cesarean delivery is reduced, and the patient's prognosis is optimized. However, if a woman is not pregnant, then the initiation of therapy can be delayed because long-term adherence with medications can be difficult, side effects are not uncommon, and prognosis is not adversely affected so long as the CD4 count and the viral load remain in a reasonable range. None of the advantages cited above can be achieved unless all women have their HIV status determined as early in pregnancy as possible.