Objective: Emotional processing differences in chronic fatigue syndrome (CFS) have been reported but have rarely been investigated experimentally. This study used self-report, observer ratings, and electrodermal responses to test hypotheses about emotion suppression and autonomic reactivity. Methods: Eighty adults with CFS and 80 healthy controls (HC) watched a distressing film clip. Half of each group were instructed to suppress their emotions and half were told to express their feelings as they wished. Their reactions were filmed and rated by independent observers. Electrodermal activity (skin conductance response) was used as a measure of sympathetic nervous system arousal. Results: CFS participants reported higher anxiety and sadness than the HC, both before and after the film. However, observers rated the CFS group as having lower emotional expression than HC in both emotional suppression and expression choice conditions. Beliefs about the unacceptability of negative emotions were associated with greater self-reported suppression. Electrodermal responses were greater in the CFS group than HC participants. Higher skin conductance responses were associated with larger posttask increases in fatigue in the CFS participants but not in the HC. Conclusions: CFS participants had lower observer-rated emotional expression than HC, despite greater distress and higher autonomic arousal. This may have implications for their ability to access social support at times of stress. As the degree of autonomic arousal was associated with short-term increases in fatigue in the CFS participants, this requires further investigation as a contributory factor for this condition.