Accumulating evidence points to significant cognitive disruption in individuals with Fibromyalgia Syndrome (FMS). This study was carried out in order to examine specific cognitive mechanisms involved in this disruption. Standardized experimental paradigms were used to examine attentional function and working memory capacity in 30 women with FMS and 30 matched controls. Cognitive function was examined using performance on these tests and between group results were analysed in the context of important psychological and behavioural measures. Performance of standardized everyday attentional tasks was impaired in the FMS group compared to controls. Working memory was also found to be impaired in this group. Stimulus interference was found to be significantly worse in the FMS group as the demands of the tasks increased. These effects were found to exist independent of the measures of mood and sleep disruption. However, when pain levels were accounted for statistically, no differences existed between groups on cognitive measures. These findings point to disrupted working memory as a specific mechanism that is disrupted in this population. The results of this study suggest that pain in FMS may play an important role in cognitive disruption. It is likely that many factors, including disrupted cognition, play a role in the reduced quality of life reported by individuals with FMS.