This study investigates learners' perceptions of the benefits and the difficulties of group work (GW) in EFL (English as a foreign language) classes. The purpose of this study is to explore the possible effects of GW, in order to better understand learners' attitudes towards GW, and to inform language teachers of students' views of using GW. A mixed-methods approach (quantitative and qualitative methods) was used to collect the required data for the study. Questionnaires were collected from 188 students in five private language institutions. These institutions specialise in teaching EFL to adult students studying in intermediate and secondary schools. From this sample, 20 students were interviewed in more detail in follow-up telephone interviews. The questionnaire examined learners' general perceptions, and the telephone interviews further explored the questionnaire findings. The findings revealed that many language learners consider the advantages of GW to be mainly related to (1) cognitive aspects, i.e. benefits that help learners in the learning process; and (2) emotional aspects, which are benefits that enhance motivation for learners. However, some learners identified difficulties, mostly related to learners' behaviours, which can result in uncooperative work in groups. These findings revealed that Saudi learners regard GW as effective in learning, but that some students' negative behaviours may prevent them from obtaining the benefits of GW.