Sperm competition between males will occur when more than one male successfully inseminates a single female and the viable sperm from different males compete for fertilization of that female's egg(s). The fertilization success of males may depend on at least two factors: the viability of sperm over time, and whether males can prevent other males from fertilizing eggs in subsequent copulations. In this study on the sand lizard, sperm did not survive in the female reproductive tract between ovulations, and sterilized males did not lower the probability of paternity for males in a second copulation occurring within 24 h. Using a genetic marker trait and DNA fingerprinting, we confirmed that multiple inseminations of different fully fertile males led to multiple paternity among offspring. The results provide evidence suggesting that neither mating order nor time between copulations has any impact on the reproductive success of first or last males. © 1993 The Association for the Study of Animal Behaviour.