Abstract: Objective: To systematically review the latent structure of the Hospital Anxiety and Depression Scale (HADS).Methods: A systematic review of the literature was conducted across Medline, ISI Web of Knowledge, CINAHL, PsycInfo and EmBase databases spanning articles published between May 2000 and May 2010. Studies conducting latent variable analysis of the HADS were included.Results: Twenty-five of the 50 reviewed studies revealed a two-factor structure, the most commonly found HADS structure. Additionally, five studies revealed unidimensional, 17 studies revealed three-factor, and two studies revealed four-factor structures. One study provided equal support for two- and three-factor structures. Different latent variable analysis methods revealed correspondingly different structures: exploratory factor analysis studies revealed primarily two-factor structures, confirmatory factor analysis studies revealed primarily three-factor structures, and item response theory studies revealed primarily unidimensional structures.Conclusion: The heterogeneous results of the current review suggest that the latent structure of the HADS is unclear, and dependent on statistical methods invoked. While the HADS has been shown to be an effective measure of emotional distress, its inability to consistently differentiate between the constructs of anxiety and depression means that its use needs to be targeted to more general measurement of distress.