Facet joint arthrography was performed in 11 patients with lumbar spondylolysis. An abnormal communication between the two facet joints bordering the separated par interarticularis was observed in nine of these patients. This communication occurred through a channel in the area of the defect. In one patient with bilateral spondylolysis of the L5 vertebra, both left adjacent apophyseal joints were observed to communicate not only with one another, but also with the contralateral facet joints, through a transverse channel joining the isthmic areas of L5. Significant pain relief following intra-articular administration of anesthetics and corticosteroids was recorded in 5 patients, for periods lasting from 2 to 10 months. Spondylolysis considerably alters the soft tissues of the adjacent facet joints. Irritation of these structures might explain certain complaints of patients with spondylolysis.