Identifying markers that are indicative of individual state, related to fitness, and which could be used to study life-history tradeoffs in wild populations is extremely difficult. Recently, it has been suggested that telomeres, the ends of eukaryote chromosomes, might be useful in this context. However, little is known of the link between telomere length and fitness in natural populations and whether it is a useful indicator of biological state. We measured average telomere length in red blood cell samples taken from a wide age range of individuals of a very long-lived and highly sexually dimorphic seabird, the southern giant petrel (Macronectes giganteus). We examined the relationship with age, sex, and subsequent survival over an 8-year period. Telomere length was longer in chicks than adults. Within the adult group, which ranged in age from 12 to 40 years, telomere length was not related to age. For the first time in birds, there was some evidence of a sex difference. Male giant petrels, which are substantially larger than females, had significantly shorter telomere lengths than females. This difference was evident from an early stage in life and is likely to relate to differences in growth trajectories. Those adults that died during the 8-year time window following the telomere length measurement had significantly shorter telomere lengths than those that survived this period, irrespective of age or sex, neither of which were significant predictors of survival. These results show that relatively short telomere length is related to future life expectancy at any adult age, demonstrating its usefulness as a state variable.