We collected data on army ant community composition- species richness and abundance- from four elevations in primary montane forest in the Monteverde zone, Costa Rica. Sample sites spanned the continental divide from 1300 m up to 1700 m on the Pacific slope, and down to 1200 m on the Atlantic slope. We sampled surface-raiding species during trail walks, and subterranean species using transects of underground bait traps. Overall rates of encountering surface raiding army ants decreased with elevation. Rates of subterranean army ant capture also decreased with elevation on the Pacific slope, but were lowest at the 1200 m Atlantic slope site. Climatic conditions (temperature, cloud cover, and precipitation) varied among sites. However, weather had no significant effects on army ant encounter rates within sites. We collected seven species in three genera of Ecitoninae, plus two species of army ant-convergent poneromorphs (genus Simopelta). Overlap of species occurrence among elevations was high. Our findings have implications for the effects of primary productivity and directional climate change on tropical montane community ecology.