Developmental stability reflects the ability of individuals to undergo stable development of their phenotype under a range of environmental conditions. Developmental instability is measured in terms of fluctuating asymmetry or phenodeviance. A negative relationship between developmental instability and fitness has figured as a prominent untested assumption in the literature. A review of available information from the literature on the relationship between developmental instability and various fitness components such as growth, fecundity, and longevity suggests that there indeed is a general negative relationship. Symmetrical individuals do generally have faster growth, higher fecundity, and better survival than do more asymmetrical individuals. These differences appear partially to arise from lower competitive ability and higher risks of predation and parasitism of asymmetrical individuals compared with more symmetrical conspecifics. The relationship between developmental stability and fitness may be either direct or indirect.