This paper reviews the research literature concerning fatigue in cancer patients, evaluating the quality of the evidence, thus helping to focus the direction and methodological rigour required in future investigations. Since fatigue in this population has been attributed to several mechanisms these will be discussed. The prevalence of fatigue in cancer patients will then be documented. An overview of what is currently understood about fatigue in cancer will follow. Based on the literature, conceptual and methodological difficulties will be described. Finally, gaps in understanding will be identified. Suggestions for future research will be formulated and potential interventions to decrease feelings of fatigue explored.