English and Arabic have different types of collocations, i.e., groups of words that go together. This study aims to explore the difficulties that Saudi undergraduate student-translators have in translating English word + preposition collocations such as verb + preposition, noun + preposition, and adjective + preposition collocations to Arabic. A corpus of faulty word + preposition collocations was collected from students-translators' graduation projects to identify the types of translation errors, translation strategies, sources of translation errors and the contexts in which the translation errors occurred. A comparison of English and Arabic word + preposition collocations showed the following categories: (1) cases were the Arabic word + preposition collocations match those of their English equivalents in form and meaning ("depend on" [Arabic characters omitted], "apologize for/to" [Arabic characters omitted], "interested in" [Arabic characters omitted]); (2) cases where a preposition is used in the English collocation but no preposition is used in the Arabic equivalent ("wait for" [Arabic characters omitted]); (3) cases where an Arabic preposition is used after a word but no such preposition is used in their English equivalent ("gave him tea" [Arabic characters omitted], "offered him a proposal" [Arabic characters omitted], "stopped participating" [Arabic characters omitted], "lack something" [Arabic characters omitted]). Results showed that the students mistranslated certain prepositions in word + preposition collocations. In 84% of the errors, the students substituted a preposition in the translation by a faulty one, in 13%, they added a preposition after an Arabic word that does not require a preposition, and in 3% they deleted a preposition from a translation that requires use of a preposition. In addition, 19% of the errors were interlingual (transfer errors from English) and 81% were intralingual due to inadequate competence in L1 (Arabic). 44% were extraneous errors, 21% were due to ignorance of Arabic language rules of preposition use and 18% were due to faulty common use of the preposition in the students' local dialect. 86% were syntactic; 11% were semantic and 3% were stylistic errors. Results are reported in detail and implications for translation pedagogy are given.