The aim of this review was to describe HIV prevalence in children and youth living on the street and subject to commercial sexual exploitation, and the studies' characteristics in terms of place, time, population, and sample design. This was a systematic review, not a meta-analysis, based on an article search in 10 electronic databases: Science Direct, MEDLINE, OVID, LILACS, Wiley InterScience, MD Consult, Springer Link, Embase, Web of Science, and Ebsco. A complementary search was also performed in the libraries of schools of public health and webpages of U.N. agencies, besides the reference lists from the selected articles. We selected observational studies focused on children and youth living on the street and subject to commercial sexual exploitation, ranging in age from 10 to 20 years, with the results for HIV prevalence rates. A total of 9,829 references were retrieved, of which 15 met the inclusion criteria and comprise this descriptive summary. Of these 15 articles, 12 were conducted in children and youth living on the street and three in children subject to commercial sexual exploitation. All 15 were cross-sectional studies. HIV prevalence in children and youth living on the street ranged from 0% in Dallas, USA and Cochabamba, Bolivia to 37.4% in St. Petersburg, Russia. In children and youth living subject to commercial sexual exploitation, prevalence ranged from 2% in Toronto, Canada to 20% in Kolkata, India. In conclusion, HIV infection is present in children and youth living on the street and subject to commercial sexual exploitation. Measures are needed for prevention, diagnosis, and treatment as a public health priority and an ethical responsibility on the part of governments and society.