We investigated habitat use by the endemic Malagasy bat Hipposideros commersoni in evergreen littoral rainforest during the wet season in 2006, in order to better inform conservation guidelines. We used radiotracking to locate roosting and foraging sites. Roosts, typically 5.4 ± 0.2 m from the ground, were always occupied by single bats and were found on branches of trees with a diameter at breast height of 8.2 ± 0.7 cm. Home range size was 31.8 ± 9.2 ha for males and 41.7 ± 12.9 ha for females. Roosts were always located within the foraging areas and only five (5.4%) of the 91 located were situated outside the sheltered littoral forest. Foraging bats made greatest use of natural, sheltered littoral forest and relatively few foraging sorties occurred beyond the forest edge. Females were not trapped during January and may undergo local movements at that time. There are no known caves in the vicinity of the study area and H. commersoni roosted only on trees. Previous studies in Madagascar have highlighted the importance of caves for bats and we now extend this to include tree roosts, within the evergreen rainforest.