In this study, the base frequency (BF) effect is explored in reading-disabled and skilled readers of Spanish. A pseudoword definition task was completed by two groups of children. The pseudowords were composed from existing stems and affixes. The results show a facilitatory BF effect, suggesting that all children benefited from this aspect of morphology. A significant effect of group was also observed, showing that skilled readers scored better than reading-disabled children. The interaction between these variables was not significant. The overall pattern of data suggests that all children benefited from morphological processing to perform the definition task but that phonological difficulties in reading-disabled children prevented them from benefitting from the BF effect as much as their skilled peers. (Contains 2 tables.)