Tarsius pumilus is one of two tarsier taxa listed as Data Deficient. Known by only three museum specimens collected over the course of the past ninety years, it is one of the most mysterious primate species. Inferences drawn from these specimens are that it is a small tarsier adapted for life in the mossy montane forests of Sulawesi at elevations of 1,800–2,200 m. To this I add the further inference from unsuccessful field surveys that is unlikely that this species duets as do other tarsiers from Sulawesi. This raises the possibility that it is not closely-related to other Sulawesian tarsiers, all of which duet, and the phylogenetic position of this species becomes highly interesting. Fossil and biogeographic evidence are consistent with the hypothesis that T. pumilus is the sister-taxon to all other extant tarsier species. If this is verified, then the small size of T. pumilus is likely to be primitive, and other extant tarsiers, small as they are, might be island giants. I argue that “mountain tarsier” is a more apt common name than “pygmy tarsier”.