The first objective was to investigate the behavioural activity in the systems of Gray's theory; these are the Behavioural Inhibition System (BIS) and Behavioural Approach System (BAS), in fibromyalgia (FM) patients. The second aim was to assess in FM patients whether there is an association between BIS or BAS with self-reported somatic symptoms. Twenty FM patients and 20 healthy controls completed questionnaire measures of BIS and BAS activity (Sensitivity to Punishment and Sensitivity to Reward Questionnaire), self-reported somatic symptoms (Somatic Symptoms Scale Revised), positive and negative affect (Positive and Negative Affect Schedule) and health status (EuroQoL Visual Analogue Scale). The results showed that FM patients had lower Sensitivity to Reward (SR) scores than controls. The SR score correlated with different somatic symptoms groups. The partial correlation (controlling for other variables measured) showed that the SR score correlated specifically with musculoskeletal symptoms. Furthermore, in regression analysis, SR score significantly predicted musculoskeletal symptoms, after controlling for other variables measured in this study. Our findings suggest that FM patients show BAS hypoactivity. This BAS activity in FM is similar to patients with depression, where a lower BAS functioning has also been found. The BAS activity predicts the musculoskeletal self-reported symptoms in FM better than other measures included in this study. Although this is a preliminary study, it suggests the importance of BAS activity in FM.