Prevalence of human immunodeficiency virus seropositivity in pediatric emergency room patients undergoing phlebotomy. Information on the prevalence of human immunodeficiency virus (HIV) infection among children and adolescents requiring medical care is sparse. A small but significant risk of seroconversion occurs in health care workers who handle blood and body fluids of patients infected with HIV. The prevalence of HIV seropositivity in children who had phlebotomy as part of emergency care was measured. Of 749 blood samples, 21 (2.8%) tested positive for HIV antibody by enzyme-linked immunosorbent assay and Western Blot analysis: 14 samples from 6 patients with hemophilia, 6 from 3 patients with acquired immunodeficiency syndrome/acquired immunodeficiency syndrome-related complex, and 1 from a patient with asthma. Of these 21 blood samples, 10 were from 4 children previously known to be HIV positive, 4 were from patients with a known parental risk factor, and 16 were from patients with known history of blood transfusion. One sample was from a children with unknown HIV status and no documented risk factors. Procedures included 9 venipunctures, 17 intravenous line placements, 1 lumbar puncture, and 1 pelvic examination. Most patients with HIV seropositivity had been known to be HIV seropositive or at significant risk for HIV seropositivity. Although the potential risk to health care workers from children without known risk factors for HIV seropositivity was small in this population, the currently recommended infection-control precautions should always be observed. 