Atractus flammigerus was described on the basis of two specimens from Java (in error). Subsequently, its lectotype was designated and the type locality restricted to Paramaribo in Suriname. Although this species has been repeatedly recorded throughout western Amazonia (mainly from Brazil and Peru), all of these records were erroneously assigned to A. flammigerus because of a considerable level of confusion with two widespread congeners (A. snethlageae and A. torquatus). To date, only nine individuals of A. flammigerus (sensu stricto) are reported in the literature on the basis of vouchered specimens. During the examination of scientific collections and fieldwork we found 12 additional specimens of this poorly known snake, expanding our knowledge on its morphological variability and distribution. In this paper, we report new localities and data on meristic, morphometric, color pattern in life and, after preservation, macro- and micro-ornamentation of dorsal scales, cranial osteology, and hemipenis morphology of A. flammigerus. We provide new diagnostic features and additional data for detailed comparisons with morphologically similar and sympatric congeners, and update the species boundaries of A. flammigerus.