Objective Fibromyalgia syndrome (FM) patients demonstrate deficits in tests of attention, executive functioning and verbal memory. We assessed the role of effort in the cognitive impairment in FM patients, alongside common symptoms of pain, fatigue and depression. Method 50 FM patients underwent a computerized cognitive assessment battery including memory, executive function, attention and information processing speed (NeuroTrax Corp.). Age and education standardized scores were computed. Effort was assessed by the Test of Memory Malingering (TOMM). FM symptoms were assessed by the Fibromyalgia Impact Questionnaire (FIQ), Widespread Pain Index (WPI) and Symptom Severity Scale (SSS), a Visual Analog Scale (VAS) of clinical pain and the Beck Depression Inventory (BDI-2). Results FM patients showed impaired performance on the memory, attention and information processing speed domains. According to the TOMM, sub-optimal effort was shown by 16% of patients. TOMM scores were not associated with pain, fatigue or depression. After controlling for effort, no significant impairment was found in memory scores; however attention and information processing speed scores remained significantly low. Multiple regressions analysis, performed in order to evaluate the contribution of effort, pain, fatigue and depression, found effort to be the only significant variable accounting for variance of cognitive scores on all domains. Conclusion The findings confirm impaired attention and processing speed in FM patients, independent of effort level. Nonetheless, the findings point to a general and strong effect of effort on neuropsychological performance in FM patients, especially in the domain of memory, emphasizes the importance of effort testing in this population.