Fractures of the os sacrum without relevant trauma history are defined as stress or insufficiency fractures and often affect the anterior pelvis. Sacral insufficiency fractures are associated with osteoporosis and occur under physiological load. In contrast, sacral stress fractures are caused by mechanical overloading. Diagnostic confirmation is delayed in many of these patients. Thus, MRI and/or CT should be performed early. Fracture stability should be evaluated by CT. MRI is the better approach to rule out fractures and is highly sensitive. It is indicated in young patients and in patients with non-specific lumbosacral pain. Nuclear imaging techniques are viable alternatives in patients with a contraindication for MRI.