Carpal tunnel injections are widely performed for diagnostic and therapeutic purposes. Injury to the median nerve is a serious and fairly common complication. There is no consensus regarding the safest injection site. The objective of this study was to determine the safest injection site based on anatomical data. During 124 endoscopic procedures for median nerve release at the carpal tunnel, we measured the distances separating the median nerve, palmaris longus (PL), flexor carpi radialis (FCR), and flexor carpi ulnaris 1 cm proximal to the wrist crease. The edge of the median nerve extended medially beyond the PL tendon in 82 (88%) hands. Thus, needle insertion within 1 cm of either edge of the PL tendon may cause median nerve injury; with injection sites located further toward the medial edge, the ulnar pedicle may be at risk. Consequently, we recommend that carpal tunnel injections be performed through the FCR tendon.