In animal societies, contrasts in reproductive skew among females are caused by variation in the frequency of reproduction by subordinates. However, despite widespread interest in the extent and causes of reproductive skew, few empirical studies have investigated the factors affecting the frequency of successful reproduction by subordinates. We tested the prediction that the extent to which dominants restrict the reproductive success of subordinates should increase as group size rises and the marginal benefits of additional helpers falls. In a long-term study of wild meerkats, Suricata suricatta, we found that dominants were more likely to evict subordinates in large groups than small ones, and that the frequency of breeding by subordinate females declined with group size, largely as a result of increases in abortion rate. The breeding frequency of subordinate females was also influenced by their age and weight, which probably reflects the capability of subordinates to breed and their ability to resist the attempts of dominants to suppress them. These findings highlight the importance of investigating variation in the benefits to dominants of controlling subordinate reproduction as well as variation in the benefits of breeding to subordinate females when attempting to understand variation in subordinate breeding success. Keywords: breeding success, cooperative breeding, fitness, meerkat, reproductive skew, Suricata suricatta.