['Few routine systems exist to test older, asymptomatic children for HIV. Testing all children in the population has high uptake but is inefficient, while testing only symptomatic children increases efficiency but misses opportunities to optimize outcomes. Testing children of HIV-infected adults in care may efficiently identify previously undiagnosed HIV-infected children before symptomatic disease.', "HIV-infected parents in HIV care in Nairobi, Kenya were systematically asked about their children's HIV status and testing history. Adults with untested children <12 years old were actively referred and offered the choice of pediatric HIV testing at home or clinic. Testing uptake and HIV prevalence were determined, as were bottlenecks in pediatric HIV testing cascade.", 'Of 10,426 HIV-infected adults interviewed, 8,287 reported having children, of whom 3,477 (42%) had children of unknown HIV status, and 611 (7%) had children <12 years of unknown HIV status. Following implementation of active referral, the rate of pediatric HIV testing increased 3.8-fold from 3.5 to 13.6 children tested per month, (RR: 3.8, 95%CI: 2.3-6.1). Of 611 eligible adults, 279 (48%) accepted referral and were screened, and 74 (14%) adults completed testing of 1 or more children. HIV prevalence among 108 tested children was 7.4% and median age was 8 years (IQR: 2-11); one child was symptomatic at testing.'] Does active referral of children of HIV-positive adults reveal high prevalence of undiagnosed HIV?