Facet joint arthrography was performed in 11 patients with lumbar [L] spondylolysis. An abnormal communication between the 2 facet joints bordering the separated pars interarticularis was observed in 9 of these patients. This communication occurred through a channel in the area of the defect. In 1 patient with bilateral spondylolysis of the L5 vertebra, both left adjacent apophyseal joints communicated with one another, and 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 2-10 mo. Spondylolysis considerably alters the soft tissues of the adjacent facet joints. Irritation of these structures might explain certain complaints of patients with spondylolysis.