A vascular nerve ablation (denervation) system includes a multiplicity of expandable needles which open around a central axis to engage the wall of a blood vessel allowing the injection of a cytotoxic or neurotoxic solution for ablating conducting tissue in and near the vessel wall of a renal artery or pulmonary vein. The expandable needles are formed of self-expanding materials and include structures which limit the distance of penetration of the injection needles into the tissue of the wall of the blood vessel.