Spondylolysis is a cleft in the pars interarticularis. It affects approximately about 5% of all population. It was postulated that it results from of a fatigue fracture caused by repeated stresses with underlying genetic or constitutional predisposition. Athletes are the most vulnerable group to be affected by spondylolysis, mainly gymnastics and fast bowlers. It is usually affects lower lumbar region and rarely occurs in upper lumbar and cervical regions. Clinically patients usually complains of back pain rarely referred to lower limb (only when facet joint hypertrophy reduces width of intervertebral foramen .little finding usually obtained. Radiologically, it could be detected using plain X-ray, and a specific radiological signs usually found in oblique views. C.T. tomogram also, is useful in its diagnosis; there is a sure sign; double defects in one cut.