Aim: To investigate whether the negative quality of life result of a large randomized exercise intervention study (BREX) was due to considerable spontaneous recovery after adjuvant treatments. Patients and Methods: The change in QoL was studied in the control patients of the BREX study (Group I) and a group of similar follow-up patients that did not participate in any intervention study (Group 2). QoL was measured by the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-C30 with the breast cancer module supplement 6 and 12 months after surgery. Results: QoL improved in both groups between 6 and 12 months after surgery. The improvement was similar in both groups for global QoL and for most of the QoL sub-scales. Conclusion: No evidence was found to support the hypothesis that participation in an exercise intervention per se significantly improves QoL. Spontaneous improvement in QoL began during the first six months after the primary treatments, which might have confounded the results of the intervention of the BREX study.