The Himalaya and Hindu Kush remain among the least scientifically explored mountain regions of Asia. Within their vertebrate fauna, pitvipers of the Gloydius himalayanus (Günther, 1864) complex have long presented taxonomic challenges due to limited sampling in remote areas and the absence of integrative analyses. Here, we present a comprehensive taxonomic revision of the G. himalayanus complex using an integrative framework that combines genetic and distributional data, external morphology, osteology, and ecological evidence. Our dataset also uniquely incorporates both newly collected material and DNA sequences obtained from 19th- and early 20th-century museum specimens, including one of the syntypes of G. himalayanus (BMNH 1946.1.19.64), underscoring the enduring value of historical collections in modern taxonomy. Analyses of four mitochondrial and three nuclear genes from populations across the western and central Himalaya and the Hindu Kush, many of which were genetically studied for the first time, recover five well-supported monophyletic lineages: G. himalayanus sensu stricto, G. chambensis, and three previously unrecognised lineages from the Hindu Kush of north-western Pakistan, the Hazara region of north-eastern Pakistan at the western margin of the Himalaya, and the Himalaya of western and central Nepal. Genetic distances in protein-coding mtDNA markers indicate species-level divergence among these lineages, ranging from 9.2–12.6% in cyt b and 8.1–14.1% in ND4, with additional support from partial allelic differentiation in phased nuclear markers, morphology, and osteology. Based on these results, we formally describe three new species, substantially expanding the known diversity of Gloydius along the southern Himalaya. To stabilise the nomenclature, we designate a lectotype for Halys himalayanus Günther. By integrating modern and historical data, this study demonstrates the lasting scientific relevance of natural history collections and emphasises the urgent need for conservation of these narrowly distributed and potentially regionally threatened mountain snakes.