This study was undertaken to contribute to the sustainable management of yam (Dioscorea sp.) diversity in Benin. We surveyed 220 farms from eight different villages in the north part of Benin. We hypothesized that the richness of yam cultivars is more related to farmers' ethnic group than to their geographical location. Cultivar diversity may differ from one ethnic group to another within a given area, but remains constant for a given ethnic group independent of its geographical location. This study identified 182 yam cultivars in the region; however, only a few farmers on a very small scale marginally produce more than 50% of that total richness. Cultivation practices as well as historical and socio–cultural determinants played important roles in the creation and maintenance of yam diversity within each ethnic group. The Bariba and the Gando ethnic groups, having developed yam cultivation since time immemorial, still hold the most diverse collection of yam varieties. The access of farmers to main roads and the availability of arable land in a given village greatly influenced the overall yam diversity in the region. This study highlighted the need to combine social determinants and geographical patterns in the conservation of agricultural diversity in Benin.