Atractus gigas was described based on a single specimen from western Andes of Ecuador. Although recently, a second specimen of A. gigas was reported close to the type locality just on the basis of photographic vouchers. During the examination of Ecuadorian and Peruvian collections, we found additional specimens of this poorly known snake. We also collected new individuals of Atractus gigas during fieldwork carried out on northeastern portion of the Peruvian Andes. In this paper, we report new specimens, localities, and data on meristic, morphometric and color pattern variation for the species. We associate the variation displayed by these character systems with sexual, geographic, and ontogenetic phenomena respectively. We provide detailed comparisons and diagnosed Atractus gigas from all others members of this highly diverse and complex genus, and comment on their natural history and ontogeny.