Orconectes neglectus, a crayfish native to the Mississippi River drainage in Arkansas, Oklahoma, Missouri, and Kansas, is reported from streams in southeastern New York for the first time. This species is the newest component of a crayfish fauna that is increasingly dominated by introduced species. Individuals of this species were collected in 1997–1999. First and second form males and females ranged in size from 7.5–40.9 mm carapace length. Ovigerous females were collected in May 1999. These data demonstrate that this species is established and reproducing in clear, rubble-bottom streams in southeastern New York. O. neglectus is readily identifiable by its distinctive coloration and color pattern; other characteristics of the rostrum, mandible, gonopod and annulus ventralis also are useful in distinguishing it from other species inhabiting northeastern North America. Currently, O. neglectus is known in the northeastern United States only from tributaries of the upper Croton River of the lower Hudson River drainage. We assume that it was introduced into the area accidentally.