There was a significant change in several cognitive variables directly following CBT. Patients focused less on MS symptoms and their interpretation of MS symptoms became less negative (embarrassment, catastrophising and damage beliefs decreased). Also, the overall perception of fatigue, measured by the B-IPQ, became more positive. Mediation analysis showed that the change in fatigue severity in the CBT group was fully mediated by the change in the perception of fatigue. Change in anxiety also co-variated with the reduction in fatigue. Discussion Changing beliefs about fatigue seems an important factor in CBT for MS fatigue. The change in fatigue is also closely related to a reduction in anxiety. The results of the present study are comparable to those investigating the effects of CBT for chronic fatigue in other conditions. Background: Fatigue is a common, distressing and disabling symptom associated with multiple sclerosis (MS). Therapist delivered, manualised cognitive behavioural therapy (CBT) has been shown to be effective in treating MS fatigue. The purpose of this study was to develop and pilot the efficacy and costeffectiveness of a web-based version of this CBT package. Methods: The MS-Invigor8 programme was developed over 9 months by a team of software developers, psychologists and people with MS. 40 patients with MS fatigue were then randomised to the web intervention in conjunction with 3 therapy phone calls (n=23) or a wait list control group (n=17). Patients were assessed using standardised self-report measures of fatigue severity and impact prerandomisation and 10 weeks later. They also completed measures of health care use and quality of life for the economics analysis. Patients in the intervention group were interviewed to see how they had experienced the treatment approach. Results: Intention-to-treat analysis showed that patients randomised to MS-Invigor8 reported significantly greater reductions on the Fatigue Scale (F(3,36) = 16.59, p<.001) and the Modified Fatigue Impact Scale (F(3,34) = 17.15, p<.001) at 10 weeks than those on the wait list. The QALY gain based on the EQ-5D was 0.015 higher in the intervention group (p=0.038), but there were no differences in service SS17b  HOW IMPORTANT IS INCREASING PHYSICAL ACTIVITY AIMING TO REDUCE  FATIGUE DURING CURATIVE CANCER TREATMENT? A RANDOMISED  CONTROLLED TRIAL OF A BRIEF NURSING INTERVENTION AND COGNITIVE  BEHAVIOUR THERAPY The assumption is that physical activity is essential to reduce fatigue. However, the mediating role of physical activity in fatigue interventions during cancer treatment has never been demonstrated.