A relationship between body size and longevity has long been appreciated within eukaryotes, especially vertebrates. For example, large size (typically body mass) is associated with increased longevity among species of mammals, but within individual species such as dogs and mice larger individuals tend to die sooner. However, whether or not there is a relationship between body size and longevity has not been well-investigated in invertebrates with the exception of mutant strains of Drosophila melanogaster in that mutant strains with a small body size being longer-lived than normal sized control strains. In this study, we examined the relationship between measures of body size and longevity in a captive population of speckled cockroaches (Nauphoeta cineria) and found that, contrary to what has previously been reported, larger cockroaches were significantly longer-lived than their smaller counterparts. Body mass, body length and pronotum width at the time of death were all significantly correlated with the age at death in a mixed population of males and females (n = 94). In addition, we found that the longevity of a historically larger population in terms of body mass and body length was also significantly greater than the test population used in this study. Taken together, these data suggest that there is a significant interaction between body size and aging in this species due to an unknown mechanism, but insulin-insulin-like growth factor signaling (IIS) has strongly been implicated in other models.