Despite their high diversity and importance as top predators in many ecosystems, the ecology of many snakes remains poorly understood. This situation is especially true at low latitudes, as few attempts have been made to quantify patterns of space usage by tropical snake species. Here, we describe macro- and microhabitat use by the abundant pit viper Bothrops asper in the lowlands of Costa Rica. Specifically, we used radiotelemetry to monitor nine female and four male adult snakes at La Selva Biological Station between 2004 and 2006. We determined macrohabitat usage and availability on the basis of the movements of individual snakes and analyzed selection using compositional analysis. Microhabitat was quantified by a series of structural characteristics, and groups of locations were compared using multivariate ANOVA and discriminant function analysis. In our study, B. asper demonstrated a positive selection for swamp habitat and avoidance of human-disturbed areas by both male and female snakes. Microhabitat usage did not differ between males and females, but did differ for all individuals between daytime observations, when snakes were typically inactive, and nocturnal observations, when snakes moved to more exposed areas and foraged using ambush tactics. Microhabitat characteristics were significantly nonrandom at both times, suggesting that B. asper actively select particular sites for both diurnal retreat and nocturnal foraging sites. These data emphasize that the contrasting ways in which animals may utilize resources at separate times or for different activities should be considered in studies of overall habitat selection.