Patients with fibromyalgia often present with increased levels of disability and physical functioning, for which the determinants are still unclear. In patients with other musculoskeletal pain syndromes, such as chronic low back pain, physical performance and disability levels are shown to be strongly associated with pain-related fear, and even stronger than pain severity. The present study was aimed at examining the role of pain-related fear and attentional processes on tolerance for physical activity in fibromyalgia patients. High and low fearful fibromyalgia patients (N=81) were requested to perform a physical task, a cognitive (reaction time) task, and a dual task in which the physical and cognitive tasks were combined. It was hypothesized that high fearful patients would terminate the physical performance task sooner than low fearful patients, and would show a greater disruption on the cognitive task. In addition, it was expected that when distracted in the dual task, high fearful patients would show improved performance on the physical task after a fear reduction instruction. The results showed that pain itself was a greater predictor of activity tolerance than pain-related fear, but that pain-related fear was the stronger predictor of reaction times on the cognitive task. Also, all groups showed equal improvement in physical performance in the dual task. The findings suggest that baseline pain acts as an occasion setter which determines the level of physical activity the patient is willing to perform, regardless of pain increase and threat-reducing instructions.