The use of exercise testing as an objective assessment of cardiorespiratory fitness in clinical oncology research has increased substantially over the past decade. However, its quality has not been assessed. We did a systematic review of studies of formal exercise testing for adults with cancer. Studies were assessed according to the American Thoracic Society/American College of Chest Physicians (ATS/ACCP) recommendations for exercise testing. Overall, the reporting of exercise-testing methods and data for adults with cancer suggests that the conduct of these tests does not comply with national and international quality guidelines. We give recommendations for exercise testing in clinical oncology research. The adoption of consistent, formal standards for methods and data reporting in exercise testing is needed to ensure high-quality research in clinical oncology. Overall, we present information for clinicians and exercise-oncology researchers who assess and care for patients with cancer.