There are over 70 species of Pachybrachis Chevrolat known from Arizona. The group hereby designated the Robust Species group, containing the largest species, consists of 14 Nearctic species: Pachybrachis ashfork Barney, Pachybrachis chaoticus Fall, Pachybrachis cylindricus Bowditch, Pachybrachis fortis Fall, Pachybrachis fuscipes Fall, Pachybrachis huachuca Barney, Pachybrachis nobilis Fall, Pachybrachis notatus Bowditch, Pachybrachis pima Barney, new species, Pachybrachis pinguescens Fall, Pachybrachis saguaro Barney, Pachybrachis sanrita Bowditch, Pachybrachis snowi Bowditch, and Pachybrachis varicolor Suffrian. Pachybrachis wenzeli Fall is synonymized under P. snowi and Pachybrachis madera Barney is synonymized under P. fortis. A key to groups of Arizona Pachybrachis species, based upon external characteristics, is provided. A key to the Robust Species is given, and a description and figure are provided for each species not previously published.