QUESTION Is sonography helpful in facet joint infiltration of the lumbar spine? METHOD The sonoanatomy of the lumbar spine and the of lumbosacral junction was examined and described in a skeleton and in 10 volunteers. One representative cross section and 3 longitudinal sections were defined. According to these results (no neurological symptoms) the possibilities of ultrasound guided infiltration of the facet joints was examined in 78 patients (36 female, 42 male, average age 55 y., 38-78 y.) with chronic low back pain and increase of pain by hyperextension. 5 ml Carbostesin partially in combination with steroids were applied to each joint. In all cases the tip of the syringe could be placed on the joint. RESULTS There were no complications, especially no infection or neurological symptoms. Application of local anaesthetics into the spinal canal could be excluded in all cases. The sonoanatomy of the lumbar spine and of the lumbosacral junction can be reproduced. Sonography allows an accurate infiltration of the facet joints of the lumbar spine. Applications into the spinal canal can be avoided. CONCLUSIONS This method is a secure and economic (extra time 2-4 min.) alternative to clinically guided infiltration. Flouroscopy guided infiltration is needed only in anatomical variations or if strictly intraarticular application is necessary.