Low back pain, secondary to a variety of musculoskeletal injuries, is common in individuals engaged in athletics. Sports-related stress reactions of the pars interarticularis are not uncommon. Stress reactions of the sacroiliac joint, on the other hand, are considered very rare. The limitations of plain radiographs and the ability of bone scintigraphy to detect stress lesions in athletes is well documented. In this paper we describe four young athletes with stress reactions of the sacroiliac region. We consider these to be uncommon but not rare, and probably self-limiting. Accurate diagnosis is important, however, to exclude more important causes of low back pain that require therapy. This type of injury also results in abnormal stresses to the lower extremities which can result in an independent and more serious injury. All sacroiliac stress reactions were unsuspected and were diagnosed only by bone scintigraphy after plain radiographs were noncontributory.