Fatigue is a frequent problem after surgical treatment of solid tumours. Aerobic exercise and psychosocial interventions have been shown to reduce the severity of this symptom in cancer patients. Therefore, we compared the effect of the two therapies on fatigue in a randomised controlled study. Seventy-two patients who underwent surgery for lung (n=27) or gastrointestinal tumours (n=42) were assigned to an aerobic exercise group (stationary biking 30 min five times weekly) or a progressive relaxation training group (45 min three times per week). Both interventions were carried out for 3 weeks. At the beginning and the end of the study, we evaluated physical, cognitive and emotional status and somatic complaints with the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Core Module (EORTC-QLQ-30) questionnaire, and maximal physical performance with an ergometric stress test. Physical performance of the training group improved significantly during the programme (9.4+/-20 watts, p=0.01) but remained unchanged in the relaxation group (1.5+/-14.8 watts, p=0.37). Fatigue and global health scores improved in both groups during the intervention (fatigue: training group 21%, relaxation group 19%; global health of both groups 19%, p for all < or =0.01); however, there was no significant difference between changes in the scores of both groups (p=0.67). We conclude that a structured aerobic training programme improves the physical performance of patients recovering from surgery for solid tumours. However, exercise is not better than progressive relaxation training for the treatment of fatigue in this setting.