The evolutionary trade-off between investment in somatic maintenance and reproduction predicts that the allocation of energy resources into reproductive traits should increase in an age-dependent manner. As an individual ages, the opportunity for future reproduction decreases; thus, despite resource limitation, individuals should allocate more resources to reproduction to maximize their potential reproductive output. Variation in the amount and timing of resources allocated to reproduction is expected to have significant fitness consequences. However, analyses of age-dependent changes in reproductive fitness often results in conflicting observations. We have examined the effect of male aging on different measures of sperm quality in Drosophila melanogaster; including sperm morphology, sperm competitiveness, reproductive output, and larval viability. Young (7-day old) and old (30-day old) RFP sperm-tagged wild type males, who were provided regular opportunities to mate during their lifetime, were used in all experiments. Sperm length measurements revealed an increase in length variation in old males, but no difference in average length between age cohorts. Single mating fertility assays, using standardized females, indicated that the total number of fertilized eggs laid does not differ in relation to male age, but did show a significant deficit in progeny surviving to eclosion for old males. Double mating competitive fertilization experiments were also conducted using a non-virgin wild type male with GFP-tagged sperm as a standard competitor. This revealed that the total number of sperm in the female reproductive tract and the seminal receptacle were reduced in matings with old males. Ongoing experiments are determining whether this is due to reduced sperm production or transfer by old males, or whether more sperm from old males is displaced by competing sperm and ejected by the female. Overall, our results document substantial fertility deficits associated with aging.