Fatigue – which is a complex, multicausal, and multidimensional subjective experience – is today the most frequently reported symptom from patients with cancer. The aim of this study was to explore the experience of fatigue in cancer patients and to describe the categories and dimensions of the symptoms. A qualitative method – grounded theory – was used. Unstructured, tape-recorded interviews with 15 cancer patients were used for data collection. The categories found in this study illustrate fatigue as a process. Three major categories were found: (1) experiences (of loss, need, malaise, psychological stress, emotional affection, abnormal weakness, difficulties in taking the initiative); (2) consequences (social limitation, affected self-esteem, affected quality of life); and (3) actions (coping). The categories were constructed on the basis of dimensions with subordinated qualities. Knowledge concerning the different expressions of fatigue is important in caring for patients with cancer. The results from this study may contribute to a better understanding of how a cancer patient can experience and express fatigue and how the symptoms may affect the patient.