Although the concept of contrastive rhetoric has received considerable attention in research on second language writing, it has not been adequately examined in a linguistically complex context such as Tunisia. This study is an attempt to contribute to the growing body of research on second language writing through investigating the validity of the Contrastive Rhetoric Hypothesis in the Tunisian context. The study is based on the assumption that the main causes of Tunisian students' deficient writing ability in the English language are transfer of Arabic and French rhetorical norms, insufficient writing ability in Arabic and/or French, lack of a well-developed metacognitive knowledge, and poor language proficiency in English. The research approach adopted is quantitative as well as qualitative. Two data collection instruments were used: a questionnaire and 150 compositions in three languages. 50 undergraduate students of English at the Institut Supérieur Des Langues de Tunis took part in the study, 25 of them were first-year students and 25 final-year students. The findings indicate that transfer is but one cause of the students' deficient writing ability and that the development of multilingual students' writing proficiency requires much more attention.