We present a study examining cognitive functions in late non-balanced bilinguals with different levels of second language proficiency. We examined in two experiments a total of 193 mono- and bilingual university students. We assessed different aspects of attention (sustained, selective and attentional switching), verbal fluency (letter and category) as well as picture-word association as a measure of language proficiency. In Experiment 2 we also compared students in their first/initial (Y1) and fourth/final (Y4) year of either language or literature studies. There were no differences between both groups in category fluency. In selective attention, bilinguals outperformed monolinguals in Y1 and this difference remained significant in Y4 despite overall improvement in both groups. Contrasting results were found in attentional switching and letter fluency: while no differences were found in Y1 in both tasks, in Y4 there was an advantage for bilinguals in attentional switching and for monolinguals in letter fluency. We conclude that overall late-acquisition non-balanced bilinguals experience similar cognitive effects as their early-acquisition balanced counterparts. However, different cognitive effects may appear at different stages of adult second language acquisition.