BACKGROUND: Although people with haematological malignancies have to endure long phases of therapy and immobility which is known to diminish their physical performance level, the advice to rest and avoid intensive exercises is still common practice. This recommendation is partly due to the severe anaemia and thrombocytopenia from which many patients suffer. The inability to perform activities of daily living restricts them, diminishes their quality of life and can influence medical therapy. OBJECTIVES: To evaluate the efficacy, safety and feasibility of aerobic physical exercise for adults suffering from haematological malignancies. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2014, Issue 1) and MEDLINE (1950 to January 2014) as well as conference proceedings for randomised controlled trials (RCTs). SELECTION CRITERIA: We included RCTs comparing an aerobic physical exercise intervention, intending to improve the oxygen system, in addition to standard care with standard care only for adults suffering from haematological malignancies. We also included studies that evaluated aerobic exercise in addition to strength training. We excluded studies that investigated the effect of training programmes that were composed of yoga, tai chi chuan, qigong or similar types of exercise. We also excluded studies exploring the influence of strength training without additive aerobic exercise. Additionally, we excluded studies assessing outcomes without any clinical impact. DATA COLLECTION AND ANALYSIS: Two review authors independently screened search results, extracted data and assessed the quality of trials. We used risk ratios (RRs) for adverse events and 100-day survival, standardised mean differences for quality of life (QoL), fatigue, and physical performance, and mean differences for anthropometric measurements. MAIN RESULTS: Our search strategies identified 1518 potentially relevant references. Of these, we included nine RCTs involving 818 participants. The potential risk of bias in these trials is unclear, due to poor reporting.The majority of participants suffered from acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML), malignant lymphoma and multiple myeloma, and six trials randomised people receiving stem cell transplantation. Mostly, the exercise intervention consisted of various walking intervention programmes with different duration and intensity levels.Our primary endpoint of overall survival (OS) was not analysed in any of the included trials, but three trials reported deceased participants during the course of the study or during the first 100 days. There is no evidence for a difference between participants exercising and those in the control group (RR 0.93; 95% CI 0.59 to 1.47; P = 0.75; 3 trials, 269 participants, moderate quality of evidence).Four trials analysed the influence of exercise intervention on quality of life (QoL). Excluding one trial with serious baseline imbalances, physical exercise improves QoL (SMD 0.26; 95% CI 0.03 to 0.49; P = 0.03; 3 trials, 291 participants, low quality of evidence). This positive effect of exercise was also found in the subscales physical functioning (SMD 0.33; 95% CI 0.13 to 0.52; P = 0.0009; 4 trials, 422 participants, moderate quality of evidence) and depression (SMD 0.25; 95% CI -0.00 to 0.50; P = 0.05; 3 trials, 249 participants, low quality of evidence). However, there is no evidence for a difference between additional exercise and standard treatment for the subscale anxiety (SMD -0.18; 95% CI -0.64 to 0.28; P = 0.45; 3 trials, 249 participants, low quality of evidence). Seven trials (692 participants) evaluated fatigue. There is moderate quality of evidence that exercise improves fatigue (SMD 0.24; 95% CI 0.08 to 0.40; P = 0.003).Eight studies evaluated various aspects of physical performance (e.g. aerobic capacity, cardiovascular fitness), but none of them could be pooled in a meta-analysis. In seven trials there is a tendency or statistically significant effect favouring the exercise group (very low quality of evidence).Three trials (266 participants) investigated serious adverse events (SAEs) (e.g. bleeding, fever, pneumonia, deep vein thrombosis, and infection), and one trial (122 participants) assessed adverse events (AEs). There is no evidence for a difference between arms in terms of SAEs (RR 1.44; 95% CI 0.96 to 2.18; P = 0.06) or AEs (RR 7.23; 95% CI 0.38 to 137.05; P = 0.19); both findings are based on low quality of evidence. AUTHORS' CONCLUSIONS: There is no evidence for differences in mortality between the exercise and control groups. Physical exercise added to standard care can improve quality of life, especially physical functioning, depression and fatigue. Currently, there is inconclusive evidence regarding anxiety, physical performance, serious adverse events and adverse events.We need further trials with more participants and longer follow-up periods to evaluate the effects of exercise intervention for people suffering from haematological malignancies. Furthermore, we need trials with overall survival as the primary outcome to determine whether the suggested benefits will translate into a survival advantage. To enhance comparability of study data, development and implementation of core sets of measuring devices would be helpful.