Stephanie J. Cole* | University of Nevada, Reno Abstract: Forensic anthropologists routinely assist law enforcement agencies in the identification of unknown human skeletal remains by creating a biological profile, an estimate of a decedent’s sex, population affinity, stature, and age at death. Currently, the only parameter of the biological profile that is routinely estimated for subadults is age at death. The primary reason for the exclusion of sex from the subadult biological profile is the ongoing belief that sex estimation can only be conducted on “adults,” a term associated with the legally defined chronological age of 18 years and older. The arbitrary designation of 18 years as the age at which sex estimation becomes tenable is problematic, because it is based upon a culturally determined definition of adulthood that is not at all grounded in biological processes pertaining to skeletal development, growth, or maturation. Because many traits used in sex estimation, specifically those of the skull and pelvis, express dimorphism as a result of puberty, they should be useful in estimating sex prior to adulthood. A new two-step method for subadult sex estimation has been developed using an ontogenetic perspective. Various skeletal maturity indicators associated with puberty are first evaluated to estimate stage of maturation. If the maturity indicators suggest puberty has commenced, traditional adult sex traits of the skull and pelvis that express dimorphism are then evaluated using modified definitions specifically for use with immature remains, and a sex estimate is generated using robust statistical analyses. The method will be made freely available to forensic practitioners as a graphical user interface, the Ontogenetic Subadult Sex Estimation System (OnSEt), providing practitioners with a user-friendly interface to include sex as part of the subadult biological profile, ultimately increasing identifications involving children in forensic contexts and improving outcomes in medicolegal death investigations.