Literature suggests that assessment may influence student learning in a positive or negative way. Despite the support for the use of portfolio assessment, relatively little is known about its effect on student learning. The purpose of this study was to evaluate the effectiveness of portfolio assessment in enhancing student learning. Students undertaking the Bachelor of Nursing programme in a University in Hong Kong participated in the study. Twelve of the students who underwent portfolio assessment described, in individual semi-structured interviews, their experience and perceptions of this form of assessment. This paper reported on the qualitative findings of the study, which employed both qualitative and quantitative methods. Three themes emerged from the students' accounts: (1) the students favoured the use of portfolio assessment; (2) the process of preparing portfolios yielded positive academic and affective outcomes; and (3) unexpected findings in the form of spontaneous collaborative learning and apparent increased interest in learning during the process of preparing portfolios for those students who lacked motivation. The qualitative findings contribute to a better understanding of the use of portfolio assessment and have implications for teaching.