In studies performed during 1986, 1987, 1990, and 1991, in the seasonally flooded forest of the Napo and Nanay river basin, we recorded seven instances of cohabitation in night monkeys, Aotus vociferans. Cohabitation refers to the sharing of a sleeping site of one species of animal with other different species of animals (Aquino & Encarnacion, 1986). We also recorded two instances of cooccupation of night monkeys with other species of nocturnal mammals. Cooccupation refers to the independent use of different sleeping sites within the same tree by two or more species of animals. This study is the first report of cooccupation within the genera Aotus. Forty-five sleeping trees with entrance holes were used by the night monkeys. In addition, one sleeping site was observed in a small concavity of the foliar sheath on a Mauritia flexuosa palm. © 1995 Japan Monkey Centre.