A 49-year-old Japanese man who had non-traumatic osteonecrosis of the femoral head with a wide necrotic lesion received transtrochanteric anterior rotational osteotomy combined with vascularized iliac bone grafting. After the bone graft (6 x 1.5 cm) was collected, the femoral head was anteriorly rotated by 90 degrees. A bone tunnel of 1.2 cm in diameter was prepared on the necrotic lesion adjacent to the intact area from the anterior part of the femoral neck to inside the femoral head. The bone graft was trimmed to the size of this bone tunnel, and inserted up to immediately below the articular surface. In the monitoring using T1-weighted magnetic resonance imaging (MRI), the low signal-intensity area between the bone graft and intact area had disappeared, and a high signal-intensity area on the weight-bearing portion of the femoral head had extended. With modifications on the insertion point of the bone graft, transtrochanteric anterior rotational osteotomy combined with vascularized iliac bone graft would be a useful means to preserve the femoral head in large non-traumatic osteonecrosis of the femoral head.