Exercise training is beneficial in healthy adults as well as patients with acquired cardiovascular disease such as coronary artery disease and heart failure. While a reduced exercise capacity is common in adults with congenital heart disease, it is not clear if these patients stand to benefit from exercise training or if it could be potentially detrimental. International recommendations encourage regular exercise in these patients but the evidence base is limited. Data from cardiopulmonary exercise testing suggest a relatively low risk of adverse events during exercise in adults with congenital heart disease. This is also supported by studies investigating the mode of death in this patient group, reporting that only a minority of patients die during exercise. Regarding the benefits of exercise training in adults with congenital heart disease only a few studies with relatively small sample sizes are available pointing to beneficial effects in selected patients. Encouragingly, in none of these short-term studies were detrimental effects observed. Therefore, adult congenital heart disease patients should not be categorically discouraged from physical activity or from participating in non-competitive sports. However, individual exercise prescriptions should be based on a comprehensive assessment of the underlying cardiac condition, possible sequelae, cardiac function, arrhythmias, pulmonary hypertension, and aortic dimensions. Furthermore, the intensity of exercise should be adapted to individual exercise capacity.