Although it has long been known that fatigue is one of the more common side-effects accompanying radiotherapy treatment, little research into the topic has been done until recently. The article reviews the recent literature highlighting our lack of understanding of what fatigue is, its aetiology, its relationship to radiotherapy treatment and how best to deal with what some patients consider to be a major problem. Finally the paper looks at the evidence of the possible benefit that can be obtained through the use of exercise, a recommendation that is currently at odds with what most radiographers within Britain are advocating to patients.