The population dynamics of Peromyscus levipes were studied in a deciduous forest in southeastern Morelos, Mexico. This study was performed at 2 sites, one having relatively little disturbance (low-disturbance site) and the other having extensive disturbance (high-disturbance site). Sampling was conducted from February 1991 through March 1992. At the low-disturbance site, the density in February 1991 was 39 individuals/ha. Although population size fluctuated temporally, it generally declined throughout the study until March 1992 (16 individuals/ha). Sex ratios of the populations were not significantly different. The reproductive pattern exhibited by P. levipes in the low-disturbance site was seasonally polyestrous. In the high-disturbance site, we caught only 6 individuals.