In the vast literature on language attrition, studies on the role of extralinguistic factors in language retention, particularly concerning foreign language (FL) skills acquired in formal instructional contexts, are scarce. We address this issue by focusing on the impact of the frequency of FL use, both extramural and in the classroom, and motivation on the retention of written production skills. FL performance of Greek learners of French (N = 19) was assessed longitudinally (at the end of the instructional period and 12 months later) across two tasks: a C-test and a written narrative task. Findings generally showed a positive influence of language use and motivation on FL retention, but their impact varied across the tasks. In the C-test, results revealed a significant beneficial effect of extramural language use for communication purposes and motivation on participants' general linguistic skills, while lexical diversity in the written narrative task was positively influenced by the learners' personal involvement when using French as well as oral FL use in the classroom. Findings allow us to deepen insights from former studies and suggest that FL attrition research should favour longitudinal approaches in order to shed light on the complex interactions between extralinguistic factors in FL retention.