Stress fracture is an overuse injury caused by muscle forces together with bending and impact forces acting on the bone, which has not adapted to the loading. The localization of stress fractures is more common in lower extremities. They are found in many other bones of the body as well. In the history of these patients a considerable amount of running exercise is usually found. The symptoms are stress pain and aching at rest after training. Typical findings are local palpation pain and edema. Sometimes tender resistance is felt. Clinically used radiological imaging methods are radiographs, scintigraphy and in some cases magnetic resonance imaging and computed tomography. The radiographs are not usually positive until 2 weeks after the onset of symptoms. With a typical history and clinical findings the radiological diagnosis causes no further problems. The corner stones of the treatment are: early identification of the symptoms, early diagnosis, a sufficiently long training pause and in special cases consultation of experts in the field. There are rare stress fractures with increased risk of a delayed union, non-union or complete fracture. Surgical treatment may be needed in some cases. The prevention of stress fractures has proved to be difficult. The risk of acquiring stress fractures is increased by running with improper shoes and in female athletes with menstrual irregularities. If running is changed to some other kind of sport, the incidence stress fractures is lower.