Dissections of five human adult cadavers revealed that the C2 spinal ganglion bears a constant relationship to the dorsal aspect of the lateral atlanto-axial joint. Radiologically, the ganglion lies extradurally opposite the midpoint of the silhouette of the lateral atlanto-axial joint space. Needles can be introduced onto this target point using fluoroscopic control and used to perform selective local anesthetic blocks of the C2 spinal nerve. This technique is applicable in cases where it is difficult to decide on clinical grounds whether occipital headaches are due to an upper cervical abnormality or are a symptom of tension headache or common migraine. In particular the technique anesthetizes the otherwise inaccessible articular branches of the median and lateral atlanto-axial joints which may be an occult source of headache.