Abstract: A modular humeral prosthesis that can be custom fitted to a particular patient by interchanging sizes of the various components by a surgeon interoperatively. The prosthesis features a humeral head having a hemispherically shaped outer surface for placement within the glenoid cavity of a human scapula, the head including on its undersurface a recessed center portion having a first cooperating connecting means. The body has a proximal end and a distal end, with the proximal end including an angled platform having a second cooperating connecting means for engagement with said first connecting means, and the distal end having a third cooperating connecting means. The body also includes a plurality of fins. A cylindrical primary stem has a proximal end and a distal end, the proximal end having a forth cooperating connecting means for engagement with said third connecting means, and the distal end having a fifth cooperating connecting means.