In the treatment of the carpal tunnel syndrome the simple division of the transverse carpal ligament sometimes causes a certain weakness of the grip strength, which takes a very long to recover. In order to avoid this inconvenience, a new technique is described consisting in an enlargement plasty of the transverse carpal ligament. The procedure is simple but precise: it consists in a zigzag incision making two flaps and suturing them over a gauge. It needs a great attention during the first stage not to accidentally wound the thenar branch of the median nerve. The division of the subcutaneous part of the ligament and the measuring of the enlargement is facilitated by a new instrument, the "Cat-Tongue Gauge" which is described there. If necessary, a pre-operative CT scan and another one performed three months later confirm the reconstruction of the ligament and the enlargement of the carpal tunnel. In 46 wrists, we observed no complications and rapid rehabilitation. Some rare painful scars can be avoided by a good location of the incision in the vertical hypothenar crease and by a precise dissection of the subcutaneous tissues. The strength of the grip seems to be recovered sooner than with the classical technique; a prospective study is started to confirm this point.