This study investigated cognitive performance in fibromyalgia syndrome (FMS) and its association with cardiovascular and clinical parameters. Thirty-five patients with FMS and 29 matched healthy controls completed a neuropsychological test measuring attention and arithmetic processing. As possible factors underlying the expected cognitive impairment, clinical pain intensity, co-morbid depression and anxiety disorders, sleep complaints, medication use, as well as blood pressure parameters were investigated. The patients’ test performance was substantially reduced, particularly in terms of lower speed of cognitive processing and restricted improvement of performance in the course of the task. While the extent of depression, anxiety, fatigue and sleep complaints was unrelated to test performance, better performance was observed in patients showing lower pain ratings and those using opiate medication. The data corroborate the presence of substantial cognitive impairment in FMS. While the experience of chronic pain is crucial in mediating the deficits, co-morbid depression, anxiety, fatigue and sleep complaints play only a subordinate role. In the control group, but not in the patients, blood pressure was inversely associated with mental performance. This finding is in line with the well known cognitive impairment in hypertension. The lack of this association in FMS confirms previous research showing aberrances in the interaction between blood pressure and central nervous function in the affected patients.