The flexor digitorum accessorius longus muscle (FDALM) is an anatomical variation that occurs with low frequency in the leg and feet. It was first described by Meckel in 1818. It arises from the tibia or fibula and extends from this towards the quadratus plantae muscle or the flexor digitorum longus muscle, crossing the medial retromalleolar canal and creating a close relationship with the elements of the tibialis posterior neurovascular bundle. A hundred and ten legs were dissected from Caucasian, adult, undefined sex cadavers, previously kept in 5% formalin solution. We developed a dissection technique in "2 times" to search for and find the flexor digitorum accessorius longus muscle, essential for the safe and successful development of surgical procedures in the region. Three cases of flexor digitorum accessorius longus muscle muscle were described. Two of them were founded in the same cadaver, in a bilateral disposition. Knowledge of this muscle variation, its embryonic origin and the possibility of finding during clinical studies and invasive procedures in the leg and feet is important for differential diagnosis in compressive pathologies.

KEY WORDS: Flexor digitorum accessorius longus muscle; Compressive pathologies; Anatomical variation.