This study investigated whether youth involved with the child welfare system in the USA are receiving formal and informal sex education. Data come from the Second National Survey of Child and Adolescent Wellbeing, a nationally representative sample of children and adolescents in contact with child protective services. Participants included young people (n = 1093, aged 11-21) involved with the child welfare system. Participants reported whether they had received formal sex education about a) abstinence only; b) contraceptives/condoms only; c) abstinence and contraceptives/condoms; or d) none. They also reported whether they knew where to access family planning services. We examined the prevalence of sex education experiences and differences in sex education access and knowledge based on participants' pregnancy history and sociodemographic characteristics. Only half (49%) of participants had received any form of formal sex education. Pregnant youth were less likely to have received any sex education compared to non-pregnant youth . 72% of adolescents who had received sex education about contraceptives/condoms reported knowing where to access family planning services compared to only 46% of adolescents who had not received this sex education . There is a pressing need for comprehensive sex education among youth involved with the child welfare system.