In this study we describe tree hole characteristics and use by the hairy-eared dwarf lemur (Allocebus trichotis) to determine habitat needs, potential functions of tree holes and sleeping group composition. We radio-tracked 6 adult individuals between April and November 2007 in the Analamazaotra Special Reserve. Tree holes were 1–9 m high (median: 7 m), in living trees measuring 26–54 cm in diameter at breast height (median: 32 cm), and could be a limiting resource. Each individual used 4 or 5 tree holes and had high nest fidelity. Animals most often slept socially in mixed-sex groups of 2–6 individuals and occasionally shared a tree hole with white-tailed tree rats (Brachytarsomys albicauda). We identified two sleeping groups: one composed of 2 adult males, 2 adult females and 2 juveniles; one composed of at least 2 adult females and 2 juveniles. Although tree holes were generally group exclusive, some intergroup sleeping was observed. Tree holes could have antipredator and thermoregulatory functions. Further research into sleeping hole availability, nest use and the degree of niche separation or competition between sympatric Cheirogaleidae and other tree hole users (e.g. endemic rodents) is needed to assess better the conservation needs of these species.