The pattern of the dorsal arterial supply of the thumb was studied by the dissection of 25 thumbs of fresh cadavers. A constant vascular axis was found, originating at the radial a. and communicating at the level of the middle third of the proximal phalanx with the arterial palmar circuit. The constant presence of this vascular axis and its connection with the palmar circuit permits the mobilisation of a dorsal metacarpal skin flap, with a distal pedicle and a reversed flow, that can be used for covering dorsal and palmar losses of substance in the thumb.