With the exception of a positive relationship between energy expenditure and number of offspring per litter, few links have been made between energy expenditure and life history attributes in mammals. The purpose of this study was to examine relationships between basal metabolic rate (BMR) and life history attributes among 26 species within the Neotomine–Peromyscine rodents. Specifically, I used independent contrasts to determine whether variation in BMR is related to variation in life history attributes that represent reproductive effort and maturation, and I determined if there is an offspring size versus offspring number trade-off. My results demonstrate that within the Neotomine–Peromyscine rodents, 1) there exists an offspring number versus offspring size trade-off whereby taxa that have a large residual number of offspring per litter have a small residual neonate mass, 2) BMR is related to this trade-off whereby taxa that have large residual BMR have small residual neonate mass and a trend towards a large number of offspring per litter, and 3) BMR is not related to total reproductive effort as represented by total litter mass, total weanling mass, or total growth rate of the litter from birth to weaning. My results suggest that high BMR facilitates a large number of small offspring per reproductive event. A large number of small offspring may confer a fitness advantage for taxa with compensatory growth mechanisms for weaned young that minimize fecundity trade-offs with small offspring size.