Mating structure can have important effects on population genetic phenomena, including inbreeding and genetic drift. However, data necessary to test predictions based on mathematical models or identify sensitivity to simplifying assumptions are difficult to collect. We used two sources of such data, pedigrees and genotypes, collected in a human-population isolate. The population studied was ... [Show full abstract] Native American and located in New Mexico. It was founded in the mid-19th century by ca. 30 individuals, primarily of Navajo origin, and its size increased steadily thereafter. A complete tribal pedigree spanning ca. 100 years (up to 1948) was collected by anthropologists starting in the 1920s. Probabilities of allelic identity by descent (IBD) within and among individuals were calculated for all generations directly from the pedigree. Wright's F-statistics were calculated from the IBD probabilities, and N-e was obtained from the statistic F-ST. Genetic typings were performed on blood samples collected from the population between 1991-1993. A second set of F-statistics were calculated from genetic typings. Genetic kinship between individuals (F-ST) and average inbreeding within individuals (F-IT) stabilized after the first two generations. However, F-ST was always greater than F-IT of the next generation, suggesting that the net effect of social practices was inbreeding avoidance. In contrast to general expectations for growing populations, N-e increased over generations due to immigration. F-statistics estimated from the genetic typings were remarkably close to pedigree estimates, suggesting a drift-migration steady state.