Reintroductions and other conservation translocations have become increasingly important conservation tools, albeit with variable success. Genetic variation is one factor, which may influence reintroduction success. Genetic variation in reintroduced populations can be augmented by increasing the number of founders or by admixing animals from different source populations. At present there is no clear understanding of the relative importance of the two. Here we address this question by combining detailed demographic information about the reintroduction history of 40 Alpine ibex populations with genetic data from neutral markers, including coalescent-based estimates of the number of genetic founders. Number of genetic founders was a better predictor of present-day genetic variation than number of released founders, indicating that differential survival of founders can substantially affect the genetic variation of reintroduced populations. The degree of admixture in the founder group had about twice as much impact on genetic variation than the number of founders. Thus, to maintain genetic variation in reintroduced populations, releasing animals from different sources might be more important than releasing many animals from a single source. This even applies to cases such as the Alpine ibex where all individuals descended from a single ancestral population, and where the admixture was only between sub-populations created by the reintroduction program and thus between populations with relatively little genetic differentiation.