Diurnal refuge-site selection was studied in eleven free-ranging brown tree snakes (Boiga irregularis) in tropical forest on the island of Guam. These nocturnal and mostly arboreal snakes were tracked using implanted radio-transmitters. A vegetation survey of the study site was performed to determine if brown treesnakes non-randomly select certain plants for refuge-sites, and thermal profiles of representative refuge sites were obtained with Hobo data loggers. Brown treesnakes preferentially used Pandanus crowns for refuge-sites. Although Pandanus represents a small proportion (3.6%) of the forest, most snakes used Pandanus most of the time for refuge. The thermal characteristics of Pandanus were comparable to those of other refuge-sites. We speculate that features of Pandanus that provide basking opportunities and moist microhabitats may be important for brown treesnakes. As Pandanus is widely distributed throughout the natural range of the brown treesnake, this genus may represent an important refuge-site for this species.