New collections of Spinomantis frogs (Amphibia: Mantellidae: Mantellinae) have been made by us in northern Madagascar, and based on these collections we here describe two new species. One species, from northeastern Madagascar, has reduced dermal spines on the limbs and resembles S. massorum, but is diagnosed based on features including its shorter snout, proportionally longer hind limbs, reduced foot webbing, and different coloration. The other species, from the Tsaratanana Massif, is most similar to S. peraccae, but can be diagnosed based on features including its much larger body size, more extensive foot webbing and different coloration. We also redescribe two other poorly known species of Spinomantis: S. brunae and S. massorum. Both these rare species had been recently described based on a single and pair of type specimens respectively, and we here report on the morphology of new comparative material. For both the new and redescribed species, we summarize information on behavior, habits, individual variation, and distribution, and we also present a morphological identification key for the entire Spinomantis genus, which now includes 12 species. The new species from the Tsaratanana Massif is known only from a single site (Befosa River). Because this site is not protected within a reserve, we propose this forest be considered for inclusion within the ongoing protected area expansion program for Madagascar.