Research on the relationship between cancer and fatigue has increased considerably in recent years. In this review, we focus on fatigue observed in patients during and after treatment for cancer, using data from empirical studies. The results from these studies indicate that fatigue is mostly studied during active treatment for cancer, and is an important problem during this period. Studies that focused on fatigue in disease-free cancer patients, although less prominent, also indicate fatigue is an important complaint in this time period. It is hard to draw conclusions with regard to the relationships between fatigue and disease- and treatment-related characteristics, because these relationships are seldom properly investigated. Relationships between fatigue and psychological, social, behavioural and physical factors have been established in several studies. However, most studies focused on the depression-fatigue association. Finally, most intervention studies to reduce fatigue appear to be successful, but the follow-up analyses are lacking.