Black vultures, Coragyps atratus, spend each night in a communal roost, and individuals sleep at several diVerent roosts over time. They feed in large aggregations at carcasses and engage in apparently cooperative behaviour within coalitions of individuals that co-occur predictably at both roosts and carcasses. Roost census data and DNA fingerprinting results were used to investigate whether black vultures tend to roost in the company of genetic relatives. Restricting the analysis to dyads of breeding adults that were the heads of known lineages and were not mated to one another, a positive correlation emerged between indices of the genetic similarity of individuals and their tendency to use the same roost on the same night. The results provide evidence of long-term associations between some closely related breeding adults, associations that appear not to be simply a consequence of natal philopatry but reflect the daily reassembly of coalitions at communal roosting sites. This social organization could facilitate the evolutionary stability of cooperation among communally roosting black vultures.