Japan Radiography and Cf and MRI scans of the lumbar spine were performed in young patients complaining of pain during extension of the lumbar spine but without neurological signs in the lower limbs. Tu-wei hted MR images in the coronal plane showed a hypointense area in the pars interarticularis before the detection of spondylolysis at that site by plain radiography or CT. We suggest that this may be useful in the early diagnosis of spondylolysis. JBoneJointSurg[Br] 1993; 75-B:764-8.