Studies of the evolution of life histories assume that there are costs to reproduction, although there is little experimental evidence for their existence. Some populations of annual meadow grass (Poa annua L.) are analyzed to test for the existence of these costs. There is a cost for high rates of reproduction early in life, mainly in lower rates and smaller plant size. There are also signs that high rates of reproduction very early in life increase subsequent risks of mortality. A possible form for the relationship is considered from a model of reproduction, growth and survival. The implications of the observed and predicted costs to the evolution of life histories in annual meadow grass are discussed.