Abstract The Colombian Speckled Tree Rat, Pattonomys semivillosus , is a little-known rodent endemic to the Lower Magdalena River basin at the Caribbean Coast of Colombia. To date it is the only species of Pattonomys documented in the country. We provide information on the rarity, and conservation status of P. semivillosus based on the current and potential distribution, population density and size using information from the literature, new records, and museum vouchers. We confirmed 66 occurrences that belong to 25 localities in six departments (Atlántico, Bolívar, Cesar, La Guajira, Magdalena, Santander, and Sucre) in northern Colombia, including 18 new localities not previously reported in the literature, mostly in the highly threatened Tropical Dry Forest ecosystem. The population density in three sites of Department of Cesar was 5.4 ind/km 2 , 5.9 ind/km 2 , and 32.4 ind/km 2 . The species matches with the Category D of rarity, and we suggest an update to the threatened assessment (from Least Concern to Near Threatened). This information will contribute to update the current IUCN assessment of the species.