The study sought to determine the psychometric properties of the Hospital Anxiety and Depression Scale (HADS) in individuals with chronic fatigue syndrome (GFS) assessed using a web-based data collection tool. Exploratory and confirmatory factor analyses were conducted on the HADS to determine its psychometric properties in 117 individuals with CFS. Seven models were tested to determine model fit to the data. Internal reliability estimations of the anxiety and depression sub-scales were found to be acceptable, however, a three-factor model was found to provide a significantly better fit to the data when compared to the bi-dimensional two-factor structure previously assumed to underpin the HADS' construct validity. The clinical utility of the HADS in the assessment of anxiety and depression in CFS appears to be fundamentally compromised by the presence of a three-dimensional underlying factor structure. Future revision of the HADS is recommended if the instrument is to be used reliably to screen CFS patients.