PurposeTo describe the impairments in physical fitness in individuals who were previously diagnosed and treated for childhood cancer.MethodsUsing the PRISMA-guidelines, a systematic search was performed in PubMed, Web of Science, and Embase using a combination of the following predefined keywords: exercise capacity OR aerobic capacity OR fitness OR cardiorespiratory fitness OR cardiopulmonary fitness OR physical fitness OR exercise testing OR exercise tolerance OR exercise OR oxygen consumption AND leukemia OR childhood cancer OR childhood cancer survivors (CCS). Studies that met our inclusion criteria were reviewed on methodological quality, while the Newcastle-Ottawa Scale was used for evidence synthesis.ResultsA total of 2644 articles were identified from the database search. After screening based on the eligibility (abstracts) and inclusion (full texts) criteria, 49 articles remained. Even though the risk-of-bias scores in the studies were generally low, yet the results from those with high-quality studies revealed that poor fitness levels were prevalent in individuals with acute lymphoblastic leukemia, brain tumor, and mixed cancer histories, compared to healthy controls.ConclusionsA global glance at CCS shows poor levels of fitness that is continuous and life-long even after active cancer treatment has ended. Nevertheless, the results presented in this review were based on a limited number of high-quality studies suggesting the need to for additional clinical trials in the topic area.