Sacral stress fractures are divided into fatigue fractures and insufficiency fractures. Fatigue fractures occur in a normal bone exposed to abnormal or repetitive stresses, whereas insufficiency fractures occur in weakened bones under normal stress and with no underlying trauma. Sacral insufficiency fractures are often overlooked causes of nonspecific lumbosacral back pain, especially in elderly women with underlying osteoporosis. In addition to old age and postmenopausal osteoporosis, other conditions which reduce bone mineral density and present risk factors for the occurrence of insufficiency fractures include: long-term glucocorticoid and bisphosphonates therapy, long-term vitamin D insufficiency and osteomalacia, renal osteodystrophy, primary hyperparathyroidism, Paget’s disease, long-term immobilisation and radiotherapy for the treatment of malignant diseases. There are no typical clinical signs to suggest sacral stress fracture. These fractures are often associated with degenerative diseases of the spine and intervertebral disc, and they are often accompanied by pre-existing osteoporotic vertebral compression fractures. Plain radiographs of the spine and pelvis, which are the first step in diagnostic imaging, are usually non-diagnostic when it comes to sacral fractures. Due to radicular pain symptoms, magnetic resonance imaging of the lumbosacral spine is the next step in diagnosis, in which sacral fractures are often revealed as accidental findings. In this paper, we shall present a case of an elderly patient with multiple comorbidities and multiple risk factors, in whose case physical therapy did not prove to be effective. During diagnostic testing, a subsequent MRI showed an accidental finding confirming the sacral fracture. Furthermore, we shall highlight the importance of early detection of sacral stress fracture in high-risk patients, in order to avoid unnecessary, and sometimes invasive, diagnostic procedures and to reduce the possibility of possible complications. The imaging method of choice for the diagnosis of sacral stress fractures is MRI.