It is frequently reported by the media and public officials that 100,000 registered sex offenders (RSOs) in the United States are “missing.” This policy note first describes the origin of this figure, which was initially derived from a 2003 informal survey of state registries conducted by a grassroots advocacy organization. Then, we explore the definitional ambiguities that complicate the process of calculating the national number of fugitive sex offenders. Finally, we present emerging research efforts to develop reliable estimates of the number and proportion of RSOs officially recorded by states as absconded, whereabouts unknown, or noncompliant with registration requirements. While such data remain limited, we find little evidence to support that 100,000 sex offenders are “missing,” using even the most inclusive definitions. Implications for policy and practice are discussed.