Carpal tunnel syndrome is the most common ductal syndrome of the upper limb, and one of the most frequent reasons for consultation in hand surgery, it affects 1% of the population, especially women, with a preference for the 40 to 70 age group. The diagnosis is clinically completed by electroneuromyography (ENMG) which makes it possible, better than the clinical examination, to judge the severity of the nerve damage and thus to guide the therapeutic indications. Carpal tunnel syndrome is often idiopathic, muscle abnormalities in the carpal tunnel are exceptional. As we relate a secondary carpal tunnel syndrome to a supernumerary muscle of fortuitous discovery on surgical operation. Therapeutic management is made of an anterior surgical approach of the wrist and then a section of anterior ligament of the carpus, a resection of the supernumerary muscle, with exoneurolysis, the evolution has been marked by an improvement in the sensitive symptomatology with progressive recovery of the gripping force.