1. Stress fractures result from muscular activity on bones rather than from direct impact upon them. 2. The fatigue variety of stress fracture occurs in normal bone when abnormal muscular tension or torsion is placed upon it. 3. The insufficiency type of stress fracture results when normal muscular stress is placed upon a bone with deficient elastic resistance. 4. Most stress fractures are of the fatigue type, occurring in an individual who engages in repetitive vigorous activity to which he is unaccustomed. 5. The biomechanics, radiologic features, and differential diagnosis were discussed and the literature was reviewed.