The estimation of the "dark figure" for any crime (the number of actual instances of a specific crime committed minus the reported cases of that crime within a population) has primarily rested on the ability to conduct random sample crime surveys. Such surveys are based on the assumption that victims experience crimes that are discrete, time-bound, and of relatively short duration. The crime of enslavement, however, presents a special challenge to estimation because it is of indeterminate duration. This challenge is compounded by the fact that victims of slavery are also often isolated by the stigma linked to sexual assault, or a sense of shame over their enslavement. Using a unique dataset, based in part on the random sample surveys of Julia Pennington et al. (2009), and extended through a process of extrapolation, this paper estimates the numbers of victims of slavery and human trafficking for thirty-seven countries in Europe. These estimated numbers of slavery victims are then compared with reported cases of slavery and trafficking for the same countries.