Importance:Approximately 1.1 million persons in the United States are currently living with HIV, and more than 700 000 persons have died of AIDS since the first cases were reported in 1981. There were approximately 38 300 new diagnoses of HIV infection in 2017. The estimated prevalence of HIV infection among persons 13 years and older in the United States is 0.4%, and data from the Centers for Disease Control and Prevention show a significant increase in HIV diagnoses starting at age 15 years. An estimated 8700 women living with HIV give birth each year in the United States. HIV can be transmitted from mother to child during pregnancy, labor, delivery, and breastfeeding. The incidence of perinatal HIV infection in the United States peaked in 1992 and has declined significantly following the implementation of routine prenatal HIV screening and the use of effective therapies and precautions to prevent mother-to-child transmission. Objective:To update the 2013 US Preventive Services Task Force (USPSTF) recommendation on screening for HIV infection in adolescents, adults, and pregnant women. Evidence Review:The USPSTF reviewed the evidence on the benefits and harms of screening for HIV infection in nonpregnant adolescents and adults, the yield of screening for HIV infection at different intervals, the effects of initiating antiretroviral therapy (ART) at a higher vs lower CD4 cell count, and the longer-term harms associated with currently recommended ART regimens. The USPSTF also reviewed the evidence on the benefits (specifically, reduced risk of mother-to-child transmission of HIV infection) and harms of screening for HIV infection in pregnant persons, the yield of repeat screening for HIV at different intervals during pregnancy, the effectiveness of currently recommended ART regimens for reducing mother-to-child transmission of HIV infection, and the harms of ART during pregnancy to the mother and infant. Findings:The USPSTF found convincing evidence that currently recommended HIV tests are highly accurate in diagnosing HIV infection. The USPSTF found convincing evidence that identification and early treatment of HIV infection is of substantial benefit in reducing the risk of AIDS-related events or death. The USPSTF found convincing evidence that the use of ART is of substantial benefit in decreasing the risk of HIV transmission to uninfected sex partners. The USPSTF also found convincing evidence that identification and treatment of pregnant women living with HIV infection is of substantial benefit in reducing the rate of mother-to-child transmission. The USPSTF found adequate evidence that ART is associated with some harms, including neuropsychiatric, renal, and hepatic harms, and an increased risk of preterm birth in pregnant women. The USPSTF concludes with high certainty that the net benefit of screening for HIV infection in adolescents, adults, and pregnant women is substantial. Conclusions and Recommendation:The USPSTF recommends screening for HIV infection in adolescents and adults aged 15 to 65 years. Younger adolescents and older adults who are at increased risk of infection should also be screened. (A recommendation) The USPSTF recommends screening for HIV infection in all pregnant persons, including those who present in labor or at delivery whose HIV status is unknown. (A recommendation).