Assessing the occurrence, geographic distribution, and spatial and temporal activity patterns of species is essential for a full understanding of their ecology, biogeography and interactions with sympatric species. Camera trapping techniques are useful in conducting such studies on mammals, as they are non-invasive and minimize disturbance of natural activity patterns. We report findings of camera trap studies of medium-large mammals on Sumaco Volcano, Ecuador, between 2010 and 2016. Sumaco Volcano lies in the heart of the Tropical Andes biodiversity hotspot and is noteworthy for having one of the most extensive, intact elevational habitat gradients in the Neotropics, ranging from the lowland rainforests of the western Amazon basin at 300 m to páramo vegetation near the volcano’s 3,800 m peak. We characterize the medium-large mammal fauna at five elevational zones on Sumaco Volcano: one located in the lower montane rainforest at approximately 1350 m, and four located in the cloud forest at approximately 1750, 2200, 2500, and 2900 m. We determined species diversity for each zone and species turnover (beta diversity) between zones. Our major conclusions are 1) that species turnover between the 1750 m and 2200 m sites was the most pronounced; however, we also found substantial turnover among upper elevation sites, suggesting that elevational differences in mammalian communities within Neotropical upper montane rainforest biomes also can be surprisingly high; and 2) that typical Amazonian lowland species occurred at all elevations (including 2900 m, far above the rainforest-cloud forest ecotone), but that no “Andean” species were found below this ecotone.