Of the six species of free-tailed bats from selected sites in northwestern Yucatan, Molossus sinaloae was taken most frequently, followed in order by Eumops glaucinus, Molossus ater, Eumops bonariensis, Promops centralis, and Tadarida laticaudata. Tile roof roost data for M. ater, M. sinaloae, and E. bonariensis showed some aggregation and, for the latter two, some roost fidelity.