This study explored whether native speakers of English and non-natives are sensitive to corpus-derived frequency of synonymous adjective-noun collocations (e.g., fatal mistake, awful mistake, and extreme mistake) and whether level of proficiency can influence this sensitivity. Both off-line (typicality rating task) and on-line (eye-movement) measures were employed. Off-line results showed that both natives and non-natives were sensitive to collocational frequency with clearer effects for non-natives as their proficiency increased. On-line, however, proficiency had no effect on sensitivity to frequency; both natives and non-natives showed early sensitivity to collocational frequency (first pass reading time). This on-line sensitivity disappeared later in processing for both groups (total reading time and fixation count). Results are discussed in light of usage-based theories of language acquisition and processing.