Twenty-one skeletally immature patients with a Grade IIB osteosarcoma about the knee were treated with a modified Van Nes rotationplasty. Fourteen patients were followed up for 4 to 10.5 years (mean followup, 8 years). Functional assessment using Enneking's method showed all had good or excellent results. No patient thought that the reconstruction affected their ability to achieve recreational, sporting, or career goals. The reconstruction is durable and is not associated with an increase in late complications.