Species with an invariant or "fixed" clutch offer a unique opportunity to examine how variation in maternal size relates to key reproductive traits, such as egg size. Theoretical models of offspring size suggest selection should operate to optimize egg size and reproductive output. However, because invariant-clutch species are unable to allocate surplus resources to additional eggs (or offspring) they may exhibit different relationships than those anticipated under theoretical expectations. To test this, I examined relationships between maternal size-egg size in Carlia rubrigularis, an invariant-clutch producing scincid lizard from tropical Australia. C. rubrigularis exhibited relative clutch masses that were lower than variant clutch size species, but which were similar to other invariant clutch size species. However, maternal size (snout-vent length and post-oviposition mass) was correlated with several clutch traits (egg mass, egg width and egg volume), but females in better condition did not produce relatively heavier eggs. These results suggest mechanistic hypotheses may best explain the observed maternal size-egg size relationships in C. rubrigularis.