This article compares an extensive collection of English loanwords into Korean with a corpus of perceptual responses to English productions by Korean students of English in Korea. The analysis selects ten obstruents situated in four prosodic contexts: initial, final, and pre- and poststress intervocalic positions. Analyses compare the mapping of the obstruents onto Korean categories in the two databases, finding a strong logistic relationship between them, which indicates a process of loanword adaptation as a regularization of the cross-language perception patterns. This conclusion is also supported by differences in the maps across the prosodic positions, wherein loanword differences are correlated with perceptual differences, and by the fact that loanword adaptations are more variable for consonants that do not have a very robust perceptual map. The data, however, also exhibit exceptional cases that apparently indicate effects of a historical lexicalization of individual forms, as well as of an explicit sociocultural standard. Thus, loanword adaptation in this case, though largely indicative of a perceptual base, is more than just synchronic perception.