Work engagement as a predictor of health is an emerging concept in occupational science and the Utrecht Work Engagement Scale (UWES) is the most popular work engagement measurement tool. However, despite its popularity, the UWES is not free from controversy concerning its factorial validity. In this paper, 21 research studies on both UWES-9 and UWES-17 factorial validity within the confirmatory factor analysis (CFA) approach have been reviewed in order to answer the question as to which of the UWES factorial structures displays greater validity. The originally proposed threefactor structure of the UWES has been recognized as superior in 6 studies. In further 6 studies, the UWES structure with 1 general factor has been found to be superior. In 8 studies, the authors have concluded that the one- and three-factor structures could be considered equivalent. One study has failed to confirm either the one- or three-factor structure of the UWES. These ambiguous results from studies focusing on the UWES factorial validity are puzzling because they not only indicate a lack of validity for the UWES as a measurement tool but might also challenge the whole concept of work engagement as a three-factor structure of dedication, vigor and absorption. Int J Occup Med Environ Health 2017;30(2):161–175