Along the northern periphery of their range, populations of the hispid cotton rat, Sigmodon hispidus, are vulnerable to major reductions in density and occasional local extinctions as a result of severe winter weather. Between our sampling periods on 3 December 2000 and 14 January 2001, 3 independent winter weather events, in conjunction with the coldest month in the state since 1983, affected central and eastern Oklahoma. We recorded a drastic decline in the population of hispid cotton rats at the Center for Subsurface and Ecological Assessment Research in central Oklahoma following these winter weather events. Densities dropped from 58.6 cotton rats/ha on 3 December 2000 to 1.2 cotton rats/ha on 14 January 2001. Although hispid cotton rat densities were declining before these winter weather events occurred, we attributed the dramatic decrease to severe winter weather and below-normal temperatures. As of 19 November 2001, the population of hispid cotton rats at the site had not recovered. Abundances between January and November 2001 ranged from 0.6 to 2.6 cotton rats/ha compared with a range of 30.1 to 112.5 during the same period in 2000. Additionally, we present evidence of populations of hispid cotton rats being affected at a statewide scale as a result of the weather in December 2000. We suspect that severe winters, such as the events described, might slow the northward advance of hispid cotton rats and serve to indirectly regulate populations along the intermediate and northern fringes of its range.