There are many ecological advantages to attaining a large body size as fast as possible (such as reduced risks of being caught by predators or increased reproductive success). However, studies in several taxa indicate that fast growth in itself can have negative as well as positive effects. There appears to be a link between accelerated growth and lifespan: rapid growth early in life is associated with impaired later performance and reduced longevity. In this review we assess the evidence for such within individual trade-offs between growth rate and lifespan, and the potential physiological mechanisms that might underlie them. We discuss the fitness implications of any reduction in lifespan, and point out that certain environmental circumstances may favour a 'grow fast and die young' strategy if this increases overall reproductive success. However, investigation of the intra-specific relationships among growth rate, lifespan and fitness is not straightforward; few studies have controlled for confounding variables such as adult body size or duration of the growth period, and none to date have measured fitness in an appropriate ecological setting. We suggest a number of experimental approaches that might allow the true relationships between growth rate and future performance to be elucidated.