This experiment investigated whether individual differences in written language proficiency among university students predict the early stages of lexical retrieval tapped by the masked form priming lexical decision task. To separate the contributions of sublexical facilitation and lexical competition to masked form priming, the effects of prime lexicality were directly compared for both transposed-letter (TL) primes (e.g., "sung SNUG"; "salb SLAB") and neighbor primes (e.g., "snag SNUG"; "sleb SLAB") in a sample of 100 university students assessed on measures of reading, spelling and vocabulary. The data for the whole sample showed facilitation from nonword primes, but inhibition from word primes. Linear mixed models including the individual difference measures showed that higher scores on a principal component that captured the shared variance among reading, spelling, and vocabulary were associated with both stronger inhibition from TL word primes and stronger facilitation from neighbor nonword primes. These findings are consistent with the lexical quality hypothesis of reading that predicts that skilled readers vary in the extent to which they have developed precisely specified orthographic representations. (Contains 8 footnotes, 2 tables, and 4 figures.)