The technique of percutaneous radiofrequency (RF) upper thoracic sympathectomy mandates an exact knowledge of the anatomical location of the sympathetic ganglia. Because conflicting descriptions are given in anatomy texts, we examined the T2 and T3 sympathetic ganglia in 48 sympathetic chains in adult cadavers to measure the exact location of the ganglia. Measurements were made relative to their distances (a) dorsal to the ventral surface of the vertebral body and (b) rostral or caudal to the midpoint of the vertebral body. Median locations of T2 and T3 ganglia were 17 to 20 mm dorsal to the ventral surface of the vertebral body and 2 mm rostral to the T1-T2 and T2-T3 vertebral bodies. The sympathetic chains lay lateral to and between the heads of the ribs at these levels. A clinical-radiographic correlation study of the sympatholytic effectiveness of various needle electrode placement sites during sympathectomy confirmed these findings. These data have been used to modify the technique of percutaneous RF sympathectomy.