This study investigates the shared versus autonomous representation of grammatical gender in the mental lexicon of Polish–Danish bilinguals. Polish has three genders (masculine, feminine, neuter), while Danish distinguishes between two (common, neuter), making their gender systems not only asymmetric but also dissimilar. Using a timed gender decision task, we tested 37 late unbalanced Polish–Danish bilinguals across varying proficiency levels and compared them to a baseline group of 38 Polish–German bilinguals, whose gender systems are symmetric and similar. The results suggested no effect of the Polish gender system on Danish, even for neuter gender, which is present in both languages. In contrast, Polish–German bilinguals showed clear lexical gender congruency effects influenced by their proficiency in German. For masculine and feminine nouns, Polish influenced gender assignment more strongly at lower German proficiency, while for neuter nouns, congruency effects only appeared at higher proficiency levels. Additionally, both groups struggled with neuter-gender assignment. These findings suggest that in the bilingual mental lexicon, asymmetric and dissimilar gender systems are represented autonomously. The results from Polish–German bilinguals are attributed to the underuse of neuter gender, potentially masking gender congruency effects for neuter nouns, and are further discussed in relation to the Parasitic Model of Vocabulary Acquisition.*