Küntscher Y-nailing is indicated for unstable proximal fractures of the femur in the elderly (5-7,10). The Williams modified Y-nail is an interlocking Y-nail that was designed to extend the indications beyond those of the Küntscher Y-nail. The Williams Y-nail was employed in three cases of subtrochanteric and subtrochanteric-intertrochanteric fractures, including one case in which there was an ipsilateral femoral shaft fracture. This procedure requires reaming and interlocking which are not performed in classic Küntscher Y-nailing. At follow-up (14-month minimum), each patient had a good clinical result and radiographic healing. Leg length shortening (maximum, 1.5 cm) occurred in two of three cases, primarily as a result of the failure to employ either a proximal or a distal interlocking screw. No other deformities have been observed. Williams Y-nailing can extend the indications of the Küntscher Y-nail to include rotationally unstable subtrochanteric fractures and associated ipsilateral femoral shaft fractures. The increased technical demands of the Williams modified Y-nail warrant cautious use depending upon the complexity of the fracture. Used properly, the Williams Y-nail may reduce the incidence of rotational and leg length deformities often experienced with other commonly used devices for unstable subtrochanteric and ipsilateral trochanteric-diaphyseal fractures of the femur.