In a study of the relative importance native speakers of French attach to different types of errors produced by second language learners, 231 native French speakers listened to 50 pairs of deviant sentences to determine which sentence in each pair contained a more serious error. The sentences contained 20 different types of errors grouped into five categories, four pertaining to grammatical features (verb errors, confusion of forms, omission, and wrong word order) and one with vocabulary-related items. Results in these error categories were compared, and it was found that inappropriate vocabulary, verb errors, and incorrect word order were considered more serious than omissions and confusion between forms belonging to the same grammatical class. Substitution of "etre" for "avoir" was considered more serious than other verb errors. Confusion of "a" and "pour" prepositions was considered more serious than other preposition confusions and more serious than pronoun confusion or masculine-feminine determiner confusion. Omission of reflexive pronouns and determiners was considered more serious than omission of prepositions and direct pronouns. Misplacement of negative particles was considered the most serious error of word order, with misplacement of object pronouns following. Results also suggest that socioeconomic class and educational background may influence native speaker judgment. The appendix provides the 50 pairs of deviant sentences. (MSE)