This study investigated learning vocabulary in group work at university in Vietnam. The students were studied in two kinds of group settings, "unassisted" and "assisted", the first consisting of five students from the same class level and the second of four from the same class and a student from a higher class. Differences were observed in both the procedures and the outcomes of vocabulary learning in the two settings. The negotiation of word meanings and forms were collaborative in the unassisted groups and expert-novice in the assisted groups. The unassisted groups used the first language to code-mix their English utterances with Vietnamese words to express their ideas. The presence of a senior student in the assisted groups virtually eliminated the use of the first language in explaining new English words. Students in the two group settings reported that they learned new words and the group discussions helped them recall and remember English words.