Heteromys anomalus is widely distributed along the Caribbean coast of South America and was generally considered the only spiny pocket mouse present in Venezuela until H. australis was reported recently from the Cordillera de Mérida. Here, I revise the spiny pocket mice of western Venezuela and compare specimens from the semi-insular Península de Paraguaná with samples from throughout the distributional area of H. anomalus. Morphological comparisons with all other species of the genus suggest that the Heteromys from Paraguaná are closely related to H. anomalus, but univariate and multivariate analyses show that they are much smaller than samples of H. anomalus. In addition, adults from Paraguaná display differences in cranial shape when compared with adults of H. anomalus. Hence, specimens from Paraguaná are here described as a new species, Heteromys oasicus, and taxonomic treatments of H. anomalus and H. australis in western Venezuela are also provided. Although the original geographic context of this case of dwarfism in body size is unknown, H. oasicus currently appears to be isolated in mesic vegetation on the low Cerro Santa Ana and Fila de Monte Cano, which lie in a matrix of tropical thorn forest. The new species represents one of the few vertebrates considered endemic to Paraguaná, but basic inventories and taxonomic studies are not yet complete in the region.