This case study describes six sonographic findings, with correlative imaging, in an adult patient with congenital Madelung deformity. Two are typical of congenital Madelung deformity: a thick volar hyperechoic band extending from the ulnar side of the distal radius toward the lunate-triquetrum area, the so-called Vickers ligament, adjacent to the radiotriquetral ligament, and a cortical defect on the ulnar and volar side of the distal radius. Other findings may be also observed, such as a narrowed distance between the Lister tubercle and the distal radioulnar joint, a dorsal subluxation of the ulnar head, an extensor tendons entrapment and pronator quadratus modifications. Although the diagnosis of congenital Madelung deformity is based usually on clinical examination, this rare malformation may remain undiscovered until adulthood. When sonography is used as the first imaging technique, the sonographic findings of congenital Madelung deformity can facilitate diagnosis and the appropriate radiographs.