Thirty fresh cadaver hands were injected with a silicone rubber compound (Microfil) and dissected to examine the vascular and neural supplies of the thenar area. In 10 specimens, a selective injection technique was used to determine the extent of skin territory nourished by the superficial palmar branch of the radial artery. The purpose of this study was to clarify the anatomic basis for clinical applications of vascularized free- or island-flap transfers from the thenar area. The superficial palmar branch of the radial artery was found in all hands; the average diameter of the branch measured at its bifurcation site was 1.4 mm (0.8 to 3.0 mm). The constant area nourished by the superficial palmar branch was an area approximately 4 x 3 cm located over the proximal parts of the abductor pollicis brevis and opponens pollicis muscles. These results indicate that a fasciocutaneous flap from the radial thenar region can be raised based on the superficial palmar branch and consistently transferred as a free flap. In 63 percent of the hands dissected, the superficial palmar branch was connected to other arteries in the palm, suggesting that the flap can be transferred as a reverse-pedicle island flap in such hands. Innervation of the flap was provided chiefly by a branch of the superficial radial nerve. The radial aspect of the thenar eminence can provide a new and useful donor source for an innervated and vascularized free- or island-flap transfer for reconstruction of various skin defects of the volar side of the fingers.