The present contribution analyzes the acquisition of subjects in French based on a longitudinal case study of a trilingual child aged 2;8–3;2 who acquired French, Italian and Spanish simultaneously. The three languages vary with respect to the null-subject property; French is traditionally characterized as a non-null-subject language, while Italian and Spanish are prototypical null-subject languages. Argument subject omissions in French are ungrammatical but frequently observed in monolingual children in early acquisitional phases, as are ungrammatical postverbal subjects which cluster with null-subjects. Bilingual children acquiring French produce fewer subject omissions and postverbal subjects. The present study also finds an acceleration effect in the trilingual child. The results are interpreted in light of a parameter setting which accounts for different verb classes at different locations with which the null-subjects occur, giving rise to ‘categorial CS’ or ‘congruent categorialization.’