Experimental research on the interface between second language vocabulary knowledge, including collocations, and translation competence is scarce. The present study investigates the role played by three determinants of collocation knowledge (knowledge level -- recall versus recognition, congruency, and constituent word types) in the accuracy of collocation translation. The study involved thirty-nine female Arabic translation students completing three tasks: an L2 (English) - L1 (Arabic) contextual translation task, a form recall test, and a form recognition test. The target items were 40 English collocations (10 adjective + noun congruent, 10 adjective + noun incongruent, 10 verb + noun congruent, and 10 verb + noun incongruent). The results of mixed-effects modelling show that producing an acceptable L1 translation was predicted by congruency and form recall knowledge of collocations while word type and form recognition knowledge made no significant contribution. These results have important implications for the teaching of collocations to student translators.