Based on a large number of specimens and genetic samples, we revise the chameleons of the phenetic Calumma nasutum species group using an integrative taxonomic approach including external and hemipenial morphology, osteology, and sequences of a mitochondrial (ND2) and a nuclear gene (c-mos). After more than 180 years of taxonomic uncertainty, the eponymous species of the group, C. nasutum, is redescribed, a lectotype is designated, and the species is assigned to a genetic clade that occurs in eastern (Anosibe An'Ala, Andasibe) and northern Madagascar (Sorata) based on morphology and osteology. The identity of C. fallax is also clarified and a lectotype is designated; it occurs at high elevation along the east coast from Andohahela (south) to Mandraka (central east). Calumma radamanus is resurrected from synonymy of C. nasutum; it lives at low elevations in eastern Madagascar from Tampolo (south) to its type locality Ambatondradama (north). However, up to five deep mitochondrial lineages and high morphological variation are identified within C. radamanus, which we consider a species complex still in need of further taxonomic revision. Furthermore, three new species of the C. nasutum group are described: C. emelinae sp. nov. is distributed in eastern Madagascar (Anosibe An'Ala in the south to Makira in the north), C. tjiasmantoi sp. nov. in southeastern Madagascar (from Andohahela in the south to Ranomafana NP in the north), and C. ratnasariae sp. nov. is known from the Bealanana District in northern Madagascar. There is only little variation in hemipenial morphology in this group; the cornucula gemina are present in all taxa except the C. radamanus complex. Due to this taxonomic revision the protection status of the treated six chameleon species needs to be newly assessed; at least two of the species appear to warrant threatened statuses.